Air conditioner making noise? Most sounds point to a specific cause. An air conditioner is never completely silent, and most of what it does is supposed to make a sound. Manufacturers publish lists of noises they expect you to hear, and that list is longer than most people realise.
The useful question is not whether yours makes a noise. It is which noise, and whether it started recently. This page sorts the normal from the not, with the manufacturer wording where it exists.
What each air conditioner noise usually means
| The noise | Most likely cause | Normal? |
|---|---|---|
| Hissing, low and steady | Refrigerant gas flowing through the system. | Yes |
| Hissing, loud, with poor cooling | Possibly a refrigerant leak. | No |
| Gurgling or swishing | Refrigerant moving through the pipework. | Yes |
| Water trickling or flowing | Condensate draining, or refrigerant. | Yes |
| Cracking or popping | The casing expanding and shrinking with temperature. | Yes |
| Ticking or clicking at start and stop | Controls switching, and the casing moving. | Yes |
| Clicking that repeats and never settles | Something contacting a fan blade, or a control cycling. | No |
| Whooshing or blowing | Air moving through the unit. | Yes |
| Whistling | Air forced through a restriction, often a dirty filter. | Usually a filter |
| Rattling | A loose panel, a loose screw, or debris in the outdoor unit. | No |
| Screeching or squealing | A fan motor bearing, or a belt on older ducted systems. | No |
| Banging or clanking | A loose or broken component inside the unit. | No |
| Buzzing, electrical | Electrical components. Worth attention. | No |
| Noise continuing after you switch off | The outdoor fan running on, or a cleaning cycle. | Usually yes |
The single most useful question is whether the noise is new. A unit that has hissed gently since the day it was installed is doing what it was built to do. A unit that started rattling last week is telling you something changed.
The noises manufacturers tell you to expect
Before assuming anything is wrong, it is worth seeing how much noise is documented as normal.
Daikin lists flowing water, blowing, ticking, whistling, clicking and clopping as normal operating sounds.
Haier documents a swishing or gurgling noise generated by refrigerant flowing in the system, and a cracking noise generated by the casing expanding or shrinking because of temperature changes.
Teco states that crackling, hissing and whooshing sounds are expected during operation, and separately describes a noise made by the expansion or contraction of the front panel due to variations in temperature, adding that it does not indicate a problem.
Panasonic lists a water flowing sound caused by refrigerant flow inside the unit, and a cracking sound caused by changes of temperature expanding and contracting the unit.
Actron Air documents a low hissing sound during operation caused by refrigerant gas flowing through both the indoor and outdoor units.
Five manufacturers, the same handful of noises. If yours is on that list and has always been there, it is not a fault.
Hissing
A low, steady hiss is refrigerant moving. Every brand above documents it and it is usually loudest just after the unit starts.
There is a version worth taking seriously. If the hiss is noticeably louder than it used to be, and the unit has stopped cooling properly, that combination can point at a refrigerant leak. Refrigerant does not get used up in normal operation, so a system that is low has lost it somewhere.
The giveaway is usually performance rather than sound. A unit low on refrigerant runs for longer and longer, cooling less and less, often over a whole season. Some units eventually report it. Kelvinator, for instance, displays EC when refrigerant leakage is detected.
A leak is not a homeowner repair and topping it up without finding the leak simply pays for the same problem twice.
Clicking and ticking
Clicking at the moment the unit starts or stops is controls switching. Daikin names both ticking and clicking in its list of normal sounds.
Clicking that repeats endlessly while the unit runs is different. The usual causes are something touching a fan blade, which produces a rhythmic tick that speeds up with fan speed, or a control cycling on and off repeatedly because it cannot settle.
The test is whether the clicking has a rhythm that matches the fan. If it does, switch the unit off and look for a leaf, a twig or a loose piece of insulation.
Rattling
Rattling is almost always mechanical and almost never refrigerant.
- A loose panel or cover on the indoor or outdoor unit, often after a service.
- Debris in the outdoor unit. Leaves, bark and seed pods collect in the base and get moved around by the fan.
- Loose screws or mounting bolts. Years of vibration work them loose.
- A failing fan bearing, which usually starts as a rattle and progresses to a grinding or screeching.
The first two are worth looking at yourself. Switch the unit off at the isolator, then look at the outdoor unit for anything obviously sitting in it. The second two are not.
Screeching, squealing and grinding
These are the noises to take seriously, because they usually come from a bearing.
A fan motor bearing that has started to fail makes a high noise that gets worse over weeks, is often worse on start up, and sometimes disappears once the motor warms. Older ducted systems with a belt driven fan can also squeal from the belt itself.
Grinding is further along the same road. A motor making that noise is usually close to seizing, and running it to failure often costs more than replacing the bearing would have.
Buzzing
An electrical buzz deserves a different response to the others on this page.
Air conditioners contain contactors and relays that make a brief noise when they operate, which is normal. A continuous buzz, particularly one that is new, is worth having looked at rather than living with.
If a buzz is accompanied by any burning smell, switch the unit off at the breaker and leave it off. Several manufacturers give exactly that instruction. Fujitsu, for example, says to stop operation immediately and disconnect the power supply at the electrical breaker in the event of a burning smell.
Why is my air conditioner making noise when it is off?
This one worries people and is usually nothing.
- The outdoor fan is running on. Daikin documents the outdoor fan continuing for another 30 to 60 seconds after shutdown for system protection, depending on the model.
- Air is still moving indoors. Panasonic describes airflow continuing after the unit is stopped as extraction of remaining heat from the indoor unit, for a maximum of 30 seconds.
- A cleaning cycle is running. Gree keeps the fan going for 10 minutes after shutdown when X FAN is on. Haier self clean runs 20 to 30 minutes. Hitachi FrostWash and Kelvinator self clean do similar. All of these run after you have switched off, by design.
- The casing is cooling down. Cracking and popping as metal and plastic contract is documented by several brands and happens most in the hour after a long run.
- Water is draining. Condensate collected during a run keeps trickling out for a while afterwards.
The one to question is a noise that continues for hours after shutdown with no cleaning cycle running. That is worth investigating.
What you can do yourself
- Clean the filters. A restricted filter makes the unit work harder and whistle, and it is a common cause of a unit that has simply got louder over time.
- Look in the outdoor unit. With the power off at the isolator, check for leaves, bark and rubbish sitting in the base.
- Check the panels. Press gently around the indoor unit fascia while it runs. If the noise changes, something is loose rather than failing.
- Note when it happens. On start up, all the time, only in heating, only after switching off. That timing is the most useful thing you can tell a technician.
- Do not remove covers. Both units contain parts that are still live or still moving.
When a noise is worth a call
- Screeching, squealing or grinding, which usually means a bearing.
- Banging or clanking, which means something is loose inside.
- A continuous electrical buzz, especially a new one.
- Any noise with a burning smell. Switch off at the breaker first.
- A louder hiss with worse cooling, which can point at refrigerant.
- A noise that appeared suddenly rather than creeping up over years.
Noise that is the unit protecting itself
Several sounds arrive at specific moments because the system is doing something deliberate, and knowing the moment tells you the cause.
The change in sound during heating
On a cold morning a reverse cycle system runs a defrost cycle, and it sounds like a fault. Heating stops, the airflow drops away, there is often a distinct flow of refrigerant through the pipework, and steam comes off the outdoor unit.
Manufacturers document both the duration and the sound. Daikin describes heat operation stopping suddenly with a flowing sound heard while the system takes frost off the outdoor unit. Teco gives four to ten minutes on its fixed speed models. Mitsubishi Heavy Industries gives five to fifteen. Fujitsu gives a maximum of fifteen.
So a burst of unusual noise partway through a July morning, followed by the unit going quiet, is the most normal thing it does all winter.
The clunk when the compressor starts
The outdoor unit has a compressor, and starting one produces a sound. On older fixed speed systems that is a distinct thump as it cuts in, repeated each time the unit cycles.
Inverter systems are quieter about it because they ramp up rather than switching on and off, which is why an older unit often sounds busier than a newer one doing the same job.
The pause that sounds like a breakdown
Almost every brand blocks a restart for about three minutes after the unit stops. Daikin, Fujitsu, Teco, Gree, Haier, Kelvinator and Actron all publish it.
During those three minutes you may hear the indoor fan and nothing else, which sounds like a unit that has half failed. It has not. It is waiting.
Noise that comes from the installation rather than the unit
Some complaints are not about the air conditioner at all, and no amount of servicing will change them.
- Vibration through the wall. An outdoor unit bolted to a bracket on a lightweight wall transmits vibration into the house. Anti vibration mounts and a ground stand are the usual answers rather than a repair.
- Duct noise on a ducted system. Air moving through undersized or sharply bent flexible duct roars at the outlet. That is a design issue set at installation.
- Outlets whistling. Closing too many zones forces the same air through fewer outlets, which raises the noise at every one of them.
- Drain gurgling. A condensate drain with a poor fall or a partly blocked line can gurgle as water backs up and releases.
The last one is worth acting on, because a drain that gurgles is often a drain on its way to overflowing.
Recording the noise before you call
This costs nothing and it changes the visit.
Take a phone video with the sound on, standing close to whichever unit is making the noise. Do it while the noise is actually happening rather than describing it afterwards, because the words people reach for do not always match what a technician expects. One person says grinding where another says rattling, and the two point at different parts.
Note three things alongside it. When the noise happens, which is start up, all the time, or after shutdown. Whether it is louder in heating or cooling. And roughly when it started, because a noise that arrived overnight has a different cause to one that crept up over two summers.
A technician who has heard the noise before arriving is looking for something specific rather than working through a list.
Telling the difference
Most of what an air conditioner does makes a noise, and five different manufacturers publish nearly the same list of sounds they expect you to hear. Hissing, gurgling, cracking, ticking and whooshing are the system working.
What changes the answer is whether the noise is new, whether it is getting worse, and whether anything else changed at the same time. A unit that started rattling last week after a windy night usually has something in the outdoor unit. A unit that has begun to screech on start up usually has a bearing on the way out.
Start with the filters and a look in the outdoor unit. Worth knowing too is how often you should service your air conditioner, since most noise complaints arrive on units that have not been looked at in years. If a symbol or a code appeared at the same time as the noise, our guide to air conditioner symbols covers what it means.
When the noise is mechanical and getting worse, that is the point where guessing costs more than asking. We send a licensed technician who works on split, multi head and ducted systems across Melbourne, and the price is confirmed before any work starts.
A heavy hum or a hard clunk from the outdoor unit often points at the compressor, and our guide to compressor replacement cost in Melbourne gives you a figure before you call.
A mechanical noise that is getting worse is worth acting on early. Find your nearest air conditioner service team, or request a quote and describe the sound.
For general advice on staying safe around electrical appliances at home, see Energy Safe Victoria.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles