Air conditioning making a noise? What each sound actually means
Air conditioning should be close to silent indoors. When it isn't, the sound itself tells you a lot. Here's how we triage noise calls over the phone before we book a visit.
Noise-to-fault translation table
| Sound | What it usually is | Urgency |
|---|---|---|
| Gurgling or trickling | Refrigerant moving, or condensate in the drain | Normal |
| Occasional click at start/stop | Relay or expansion of the casing | Normal |
| Rattling indoors | Loose fascia clip, filter not seated, or debris on the fan wheel | Low — fix soon |
| Rattling outdoors | Loose panel screws or the unit not level on its brackets | Low |
| Buzzing or humming, no start | Failing capacitor or contactor | High — turn it off |
| Screech or squeal | Fan bearing on the way out | High |
| Grinding | Bearing failure or fan hitting the housing | Stop using it |
| Hissing | Refrigerant leak | Turn off, book an engineer |
| Bubbling with a chemical smell | Leak at a joint | Turn off immediately |
The two you can usually fix yourself
- Rattling indoor unit: open the fascia, remove and refit both filters — nine times out of ten one isn't clipped home. Close the fascia until both catches click.
- Vibrating outdoor unit: check the four bracket bolts are tight and that anti-vibration mounts are actually fitted. A unit bolted straight to a wall without rubber mounts will transmit hum into the house — and into your neighbour's.
Noise levels to expect from a good install
A modern wall unit runs at 19–24 dB(A) on low indoors, and a domestic outdoor unit at 45–52 dB(A) at one metre. If yours is noticeably louder than a fridge indoors, something is wrong with the fit rather than the machine.
If your concern is what the neighbours can hear rather than what you can, read our noise and neighbours guide — it covers the 1993 Act, the boundary test and siting fixes.
What a noise repair costs
| Fix | Typical price |
|---|---|
| Refit fascia / filters / tighten panels | Often free on a service visit |
| Anti-vibration mounts retrofitted | £90 – £160 |
| Fan capacitor | £140 – £220 |
| Fan motor | £180 – £340 |
| Relocate outdoor unit to a quieter position | £350 – £700 |
FAQ
Is gurgling from an air conditioner normal?
Yes — it's refrigerant or condensate moving. Constant loud gurgling with poor cooling can indicate low charge.
Why is my outdoor air conditioning unit vibrating the wall?
Almost always missing or compressed anti-vibration mounts, or brackets bolted into a hollow wall without proper fixings. Both are fixable.
Should I keep using an air conditioner that's grinding?
No. Grinding usually means a failing bearing, and running it risks destroying the fan motor and housing.
Is a hissing air conditioner dangerous?
Hissing suggests a refrigerant leak. Turn the unit off, ventilate the room and call an F-Gas registered engineer.
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