How to record your AC for a useful result
Garbage in, garbage out, and that goes for AC noises too. A clean 10 to 30 second clip of the actual problem sound gives the analyzer, and any technician you eventually call, something real to work with, instead of you doing your best compressor impression over the phone.
- Pick the source. Decide whether the noise comes from the indoor unit, the vents, the outdoor unit or a window unit. If you cannot tell, record each separately.
- Record while it is happening. Include the start-up and a stretch of steady running. If the noise only appears at shutdown, capture that instead.
- Keep a safe distance. About an arm's length from an indoor unit or vent is fine. Stay a few feet back from an outdoor unit's fan grille, and never reach into or lean over a running unit.
- Cut background noise. Turn off the TV, other fans and conversation. Outdoors, shield the microphone from wind or record during a calm moment.
- Use a plain voice recorder. Video-call and meeting apps are very good at filtering out steady background noise, which is great for hiding your dog's barking and terrible for hiding the exact sound you're trying to capture.
- Write down the context. Note when it happens, how long it lasts, the type and age of the system, and the last time the filter or unit was serviced. A technician will ask, and "it's been doing a thing, kind of a whoosh, I dunno" is not a diagnosis.
AC noises and what they usually mean
Unhelpfully, air conditioners don't come with subtitles. There is no single sound a broken unit makes; what you hear depends on which part is failing, and most sounds have more than one possible cause. This guide lists the common ones, what you can safely check yourself, and when to stop and hand the problem to someone with a multimeter. Think of it as WebMD, but for machines, and with better odds it isn't fatal. It is general guidance and cannot confirm a fault in your particular unit.
| Sound | Common causes | Urgency |
|---|---|---|
| Rattling or vibrating | Loose panels, debris in the outdoor unit, a loose fan blade, lines touching the frame | Usually minor |
| Buzzing | Failing capacitor, chattering contactor, loose wiring, debris hitting the fan | Get it checked |
| Humming | A soft hum is normal; a louder or new hum can mean a failing capacitor or motor | Get it checked |
| Clicking | One click at start and stop is normal; repeated clicking points to the thermostat, a relay or the contactor | Get it checked |
| Hissing | A brief hiss at shutdown is normal; a continuous hiss can mean a refrigerant or duct leak | Get it checked |
| Squealing or screeching | Worn motor or blower bearings, a slipping belt, or compressor trouble | Get it checked |
| Grinding | Failed motor bearings, a blower wheel rubbing its housing, or internal compressor wear | Switch off, call a pro |
| Banging, knocking or clanking | A loose or unbalanced blower wheel, a broken fan part, or loose compressor parts | Switch off, call a pro |
| Whistling | Restricted airflow, a dirty filter, blocked vents or leaky ducts | Usually minor |
| Gurgling or bubbling | A partly blocked condensate drain, air in the drain line, or normal refrigerant flow | Usually minor |
Rattling or vibrating AC noise
Sounds like: loose change in a dryer, or a maraca having an existential crisis.
- Common causes
- Loose access panels or screws, leaves or small debris in the outdoor unit, a loose fan blade or motor mount, or copper lines and ducts touching the frame or each other. On a window unit, a loose mounting bracket or window frame is the usual suspect.
- Safe checks
- Switch the unit off at the thermostat and at the outdoor disconnect or breaker, then look for debris and visibly loose panels. Check that the unit sits level and that nothing is touching the refrigerant lines.
- Call a technician if
- The rattle continues after you clear debris and tighten exterior panels, or you can see a fan blade wobble.
Buzzing AC noise
Sounds like: an angry mosquito that's been wired into your electrical panel.
- Common causes
- A weak or failing capacitor, a worn or chattering contactor, loose electrical connections, debris touching the fan, or a compressor that is struggling to start.
- Safe checks
- Replace a dirty filter, since restricted airflow strains the blower, and look for debris around the outdoor fan grille. Do not open electrical panels: capacitors can hold a dangerous charge even with the power off.
- Call a technician if
- The buzzing is loud, comes with a tripped breaker or weak cooling, or the fan is not turning while the unit buzzes.
Humming AC noise
Sounds like: a monk meditating, right up until it isn't.
- Common causes
- A soft, steady hum from the compressor and fan is normal. A louder or new hum, especially when the outdoor fan is not spinning, often points to a failing capacitor or motor. Loose parts can also turn a normal hum into a drone.
- Safe checks
- Note whether the outdoor fan is turning. Never try to spin it by hand or with a stick, and do not touch anything inside the unit.
- Call a technician if
- The unit hums but the fan does not turn, cooling has dropped, or the hum has grown noticeably louder over a few days.
Clicking AC noise
Sounds like: a clock that only ever learned the "tick," never the "tock."
- Common causes
- One click when the system starts or stops is normal. Repeated clicking can come from a failing thermostat, relay, control board or contactor. A steady tick with each fan rotation usually means debris or a bent blade touching the fan, while ticking from ducts as they warm and cool is harmless.
- Safe checks
- Replace the thermostat batteries, confirm the thermostat is set to cool and below room temperature, and look for debris near the fan.
- Call a technician if
- Clicking continues for more than a few seconds, repeats in rapid bursts, or the AC does not start after clicking.
Hissing AC noise
Sounds like: a small, disgruntled snake has taken up residence in your ductwork.
- Common causes
- A short hiss when the compressor stops is usually refrigerant pressures equalizing. A hiss that continues, especially with weak cooling or ice on the coil or refrigerant lines, can point to a refrigerant leak. Leaky ductwork also hisses, and a heat pump in defrost mode whooshes and may steam.
- Safe checks
- Note whether the hiss stops soon after the unit shuts off, and check for ice on the indoor coil or the outdoor lines. Replace a dirty filter and open all vents.
- Call a technician if
- The hiss is continuous, cooling is weak, or there is ice. Handling refrigerant requires a certified technician in the US and many other countries, so do not try to top it up yourself.
Squealing or screeching AC noise
Sounds like: a dolphin that really, truly does not want to be in your ceiling.
- Common causes
- Dry or worn motor or blower bearings, a slipping belt on older belt-driven blowers, or a fan blade rubbing its housing. A sharp screech from the outdoor unit when the compressor starts can signal serious compressor trouble.
- Safe checks
- Work out whether the sound comes from the indoor or outdoor unit, and replace a dirty filter. If it is a screech from the outdoor unit, leave the system off.
- Call a technician if
- It persists beyond a cycle or two. Running on worn bearings can damage the motor.
Grinding AC noise
Sounds like: a coffee grinder that swallowed a fork. Not a good sign in either machine.
- Common causes
- Failed motor or blower bearings, a blower wheel rubbing its housing, or wear inside the compressor.
- Safe checks
- Switch the system off. Grinding means metal is contacting metal, so there is no safe do-it-yourself test while it runs.
- Call a technician if
- Always. Continued running can turn a bearing replacement into a motor or compressor replacement.
Banging, knocking or clanking AC noise
Sounds like: someone's trying to get your attention. They are. It's your compressor.
- Common causes
- A loose or unbalanced blower wheel, a broken fan blade or motor mount, or loose parts inside the compressor. A single pop or bang from ductwork as it warms or cools is usually harmless.
- Safe checks
- Switch the system off and note whether the bang repeats with each fan rotation or only at start and stop. A one-off duct pop at start or stop is common.
- Call a technician if
- You hear repeated metallic banging or knocking, or any bang along with vibration you can feel.
Whistling AC noise
Sounds like: a tea kettle that never got the memo about turning itself off.
- Common causes
- Restricted airflow is the most common cause: a clogged filter, closed or blocked vents, or undersized return grilles. Duct leaks also whistle, and occasionally so does a refrigerant leak.
- Safe checks
- Replace or clean the filter, open every vent and clear furniture away from return grilles.
- Call a technician if
- The whistle persists after those airflow fixes, or cooling is weak.
Gurgling or bubbling AC noise
Sounds like: your AC clearing its throat before it says something important.
- Common causes
- A partially blocked condensate drain, air in the drain line, or normal refrigerant flow, which is common for a few moments when a mini-split starts.
- Safe checks
- Look for water backing up in the drain pan or dripping from the indoor unit, and check that the drain outlet is not blocked.
- Call a technician if
- Water is leaking, or the gurgling is constant and cooling is weak.
What does a broken AC compressor sound like?
Think of the compressor as your AC's heart: it sits in the outdoor unit of a central or split system, quietly pumping away, and a healthy one makes little more than a steady, low hum. When it starts failing, though, it tends to make its feelings known. The sound usually falls into one of these patterns:
- Grinding or screeching
- Worn bearings or internal wear. This is the sound most closely associated with a failing compressor. Switch the system off and call a technician.
- Knocking or banging from inside the casing
- Loose or broken internal parts. A rattle from the outer casing is more often loose panels or mounting feet, so check those first with the power off.
- Loud hum or buzz, then nothing
- The compressor is trying to start and cannot, sometimes with a tripped breaker. This can be a seized compressor, but a weak start capacitor is a common cause.
- Repeated clicking, no start
- More often a contactor, capacitor or control problem than the compressor itself.
- Hissing or bubbling with weak cooling
- Can indicate a refrigerant leak. Low refrigerant puts extra strain on a compressor, but the leak is the problem to fix first.
Do not assume the compressor is dead from sound alone. Capacitors, contactors and fan motors commonly fail and can make similar noises, and they are usually far cheaper to replace. Compressor replacement is a major repair, so get a technician's diagnosis, and a second opinion if the quote is large, before committing.
Why is my AC making noise when it starts, runs or stops?
A little detective work goes a long way here: when a noise happens is often just as telling as what it sounds like. Use this table to narrow down the likely culprit, then go read the matching sound above for the full story.
| When you hear it | Where to look first |
|---|---|
| Only when the AC starts | A failing start capacitor or contactor, a hard-starting compressor, or a loose mount. One click or a brief whoosh is normal. |
| Only while it runs | Fan blade or bearings, loose panels, or restricted airflow from a dirty filter or blocked vents. |
| Only when it stops | A short hiss or gurgle is normal pressure equalizing. A bang can be ducts contracting or a loose part. |
| Louder at higher fan speed | A blower or airflow problem: a dirty filter, an unbalanced blower wheel or a duct restriction. |
| Mostly at night | The house is quieter, so normal sounds stand out, and ducts contract as temperatures drop and can tick or pop. |
| Along with weak cooling or ice | Restricted airflow or a refrigerant problem. Have a technician inspect it. |
Is it normal for an AC to make noise?
Before you spiral: your AC is a machine, not a librarian, so it's allowed to make some noise while it works. These sounds are usually nothing to worry about:
- The whoosh of moving air and a soft fan and compressor hum while running
- A single click when the system starts or stops
- A brief hiss or gurgle at start-up or shutdown as refrigerant pressures settle
- Ticking or popping from ductwork as it warms and cools
- Water trickling through a condensate line or a window unit's drain
- Whooshing and visible steam from a heat pump's outdoor unit during defrost
A sound that is new, louder, more frequent, or that comes with weaker cooling, a smell or a tripped breaker is worth checking even if it resembles something on this list. When in doubt, trust your gut: if it makes you go "huh, that's new," it's new.
AC noises by type of unit
The same sound can mean very different things depending on the kind of air conditioner making it. A rattle from a window unit and a rattle from a central AC's outdoor unit are basically distant cousins: related, but living very different lives.
- Central (split) AC
- Indoor noises (blower, ducts, filter, drain) and outdoor noises (compressor, fan, contactor, capacitor) have different causes. Decide which side the sound comes from first and record each side separately.
- Window unit
- Most rattles come from the mounting: a loose bracket, window frame or side panel. A fan blade rubbing its shroud also rattles, and the compressor hum is more noticeable because the unit is in the room with you.
- Mini-split
- Gurgling and clicking at start-up are common as refrigerant flows and louvers move. Whistling often points to a dirty filter, and dirt on the blower wheel can unbalance it and cause a wobble or chirp.
- Portable AC
- Portable units keep the compressor and fans in the room, so they are louder by design. Rattling often comes from loose exhaust hose connections or the window vent kit, and sloshing or gurgling from the condensate reservoir or drain, if yours has one.
- Heat pump
- In heating mode, expect whooshing and visible steam from the outdoor unit during defrost, and a whoosh when the reversing valve changes mode.
Car AC making a noise?
A car's air conditioning is a different system from a home unit: it uses a belt-driven compressor. A click when the compressor clutch engages is normal, squealing often points to a belt, and grinding or rattling can point to a worn compressor bearing. For vehicle noises, try Carithm AI's car and engine sound diagnosis.
How the analyzer works and what it cannot do
No magic, no crystal ball, just pattern matching. You record or upload a clip, the AI listens for pitch, rhythm and other acoustic fingerprints, and hands back a shortlist of likely culprits. Think of it as a very fast, slightly tired-sounding first opinion: useful for deciding what to check yourself and what to tell a technician, not a replacement for either.
It's not psychic, though. Keep these limits in mind before treating a result as gospel:
- It cannot measure refrigerant pressure, electrical readings or airflow, which are the measurements a technician uses to confirm a fault.
- Wind, echo and other appliances in the recording reduce accuracy.
- Different faults can sound alike, for example a failing capacitor and a worn contactor.
- It does not know your unit's make, age or service history.
- It cannot tell you whether it is safe to keep running the system. When in doubt, switch it off.
Looking to diagnose a car or engine noise?
Turns out weird noises aren't just an AC thing. Carithm AI also analyzes car and engine sounds to help identify possible mechanical problems.
AC sound diagnosis FAQ
The questions everyone asks, answered without the upsell.
Can AI diagnose an AC problem by sound?
AI can analyze the acoustic patterns in a recording and suggest causes that commonly produce that kind of sound. It cannot measure pressure, voltage or airflow, so treat the result as a starting point and have a qualified HVAC technician confirm anything involving electrical parts, refrigerant or the compressor.
How do I record my AC noise so the analysis is useful?
Use your phone's voice recorder, stay about an arm's length from the indoor unit or a few feet back from the outdoor unit, and record 10 to 30 seconds while the noise is happening. Turn off TVs and fans, and never reach into or lean over a running unit. The recording checklist has more detail.
Is it normal for an air conditioner to make noise?
Yes, some sound is normal: airflow, a soft fan and compressor hum, a click when the system starts or stops, and brief hissing or gurgling as refrigerant pressures settle. A new sound, a louder sound, or one that comes with weak cooling, a burning smell or a tripped breaker is worth investigating. See the list of normal AC sounds.
Why is my AC making a buzzing or humming noise?
Common causes include a failing capacitor, a worn contactor, a motor working against a blocked or seized fan, or loose electrical connections. If the outdoor fan is not turning while the unit hums, switch the AC off and call a technician. Do not open electrical panels, because capacitors can hold a charge even when the power is off. Details for buzzing and humming.
What does a broken AC compressor sound like?
A failing compressor is most often linked to grinding or screeching, loud knocking from inside the outdoor unit, or a loud hum or buzz where the unit tries to start and fails, sometimes with a tripped breaker. Similar noises often come from a capacitor, contactor or fan motor, which are usually cheaper to fix, so get a technician's diagnosis before assuming the compressor has failed. See compressor sounds.
Why does my AC make a loud noise when it starts?
A single click or a brief whoosh is normal. A loud bang, buzz or grinding at start-up can point to a failing start capacitor, a hard-starting compressor, a loose mount or debris in the fan. Note whether it happens every cycle and get it checked if it does. See how timing narrows down the cause.
Does a hissing AC always mean a refrigerant leak?
No. A short hiss when the compressor stops is usually pressure equalizing, and leaky ducts can hiss too. A hiss that continues, especially with weak cooling or ice on the coil or refrigerant lines, deserves a technician's attention. Refrigerant work requires a certified technician, so do not try to top it up yourself.
Can I keep running my AC if it is making a strange noise?
It depends on the sound. Switch it off for grinding, screeching, loud banging, a burning smell, smoke, sparks or a breaker that keeps tripping. A light rattle or whistle is usually less urgent: check the filter and the outdoor unit for obstructions and arrange a service visit if it continues. See when to switch off.
Does the analyzer work for window, portable and mini-split units?
Yes. The tool analyzes recordings from air conditioners and HVAC equipment, and the sounds differ by type. The guide to noises by AC type explains what is typical for each.
Is the AC sound diagnosis tool free, and do I need an app?
It is free and runs in your web browser on a phone or computer, with no app download. To record, your browser will ask for microphone permission.
How accurate is the analysis?
It returns possible causes rather than a confirmed diagnosis, and accuracy depends on recording quality and on how distinctive the fault sounds. Several problems can sound alike: a failing capacitor and a worn contactor can both buzz. Use the result as a lead and confirm it with a technician.
Further reading
- U.S. Department of Energy: Home Cooling 101, a guide to how air conditioners work and common problems, including low or leaking refrigerant.
- U.S. EPA: Section 608 technician certification requirements, which explains why refrigerant work must be done by certified technicians in the US.
About this page
Who: Carithm AI builds AI tools that analyze mechanical sounds. We started with cars and engines, because those complain loudly too, and have since branched out into air conditioners and HVAC equipment.
Why: Because "it's making a weird noise" is one of the least useful sentences in the English language, and we wanted to help turn it into something actionable.
How: The analyzer is described above, including its limits. This page shows the date it was last updated, and safety guidance is written to err on the side of switching the system off. More about Carithm AI.
Important: AI sound analysis is an indication and not a substitute for inspection by a qualified HVAC technician. Electrical, refrigerant and mechanical faults should be professionally inspected when necessary.