Noisy Aircon: What's Actually Wrong?

Aircon noise is annoying but informative. Each sound type points to a different fault — and almost all of them are a quick aircon repair if diagnosed early. This guide maps the five most common noise types to their typical causes and fixes, so you can make a useful WhatsApp message when you book. If the unit is also blowing warm air, cross-check with our guide on why your aircon is not cold.

Rattling: loose panel or fan wheel

Most likely cause: loose front panel or unbalanced fan wheel. Typical fix: re-clip panel (free during routine service) or fan wheel rebalance (S$80–S$120).

A rattling noise — irregular, quick, often louder at certain fan speeds — usually means something is loose. The most common culprits:

• Front panel clips that have worked loose over years
• Filter that hasn’t been seated correctly after cleaning
• Fan wheel imbalance from caked dust on certain blades
• Loose screw somewhere in the casing

The first two are usually fixable in 5 minutes during routine servicing. The fan wheel rebalance involves removing the wheel, cleaning it thoroughly, and refitting — included in chemical wash work.

If rattling appears suddenly and is loud, switch off and check — it could be a cracked fan blade, which needs immediate attention before pieces break free.

Buzzing: capacitor or contactor problem

Most likely cause: failing capacitor or contactor in the outdoor condenser. Typical fix: capacitor S$120, contactor S$100.

A buzzing noise from the outdoor unit (the box on the external wall) usually means an electrical component is struggling. The two prime suspects:

• Failing start capacitor — the compressor is trying to start but doesn’t have enough surge capacity. You may also notice the compressor humming without actually starting.
• Failing contactor — the relay that switches power to the compressor is sticking or buzzing under load.

Both are common 6–10 year wear items. Both are S$80 diagnosis + the part. Both should be fixed within 24 hours of noticing — running the system with a failing capacitor will eventually burn out the compressor, which is a much more expensive failure.

Whistling: refrigerant leak or duct gap

Most likely cause: refrigerant leak at a copper joint, or air leak around the wall conduit. Typical fix: leak repair S$200+, conduit reseal S$80.

A continuous high-pitched whistle, especially audible at night when the room is quiet, usually points to a small refrigerant leak at a brazed copper joint. The high-pressure refrigerant escapes through the pinhole, producing the whistling sound.

Less commonly, a similar whistling can come from an air leak around where the copper pipe enters the wall — the conduit foam or putty seal has cracked.

A leak repair on a copper joint is more expensive than a top-up, but it’s the right fix — topping up a leaking system buys weeks at most.

Clicking: thermostat relay or expansion valve

Most likely cause: thermostat relay clicking on/off, or expansion valve operating normally. Typical fix: usually no fix needed (normal operation), or thermostat sensor S$80.

A regular click — once every 30 seconds, or once every few minutes — is usually normal operation. The thermostat relay clicks when the unit cycles, and the electronic expansion valve clicks when it adjusts refrigerant flow.

A click that keeps repeating rapidly (every 1–2 seconds) is not normal and indicates the relay is faulty. Switch off and book a diagnosis.

Gurgling: refrigerant flow or drain issue

Most likely cause: low refrigerant or air in the drain pipe. Typical fix: refrigerant top-up S$80+ or drain flush S$80.

A gurgling sound — like water moving through a partly filled pipe — can come from two places:

• The refrigerant lines if the system is low on gas, allowing pockets to form
• The drain pipe if condensate isn’t flowing freely

The two are easy to tell apart: refrigerant gurgle is heard near the indoor unit during cooling; drain gurgle is heard near the drain outlet (usually at the wall conduit).

For refrigerant gurgle: pressure test, leak find, top-up. For drain gurgle: pressure flush of the pipe.

Quick noise-to-fix matrix

What to send when you book

A 5-second voice memo of the noise from your phone is often all we need to narrow it down before the technician arrives. WhatsApp +65 9182 5233 with:

• The audio clip
• Whether the noise is from the indoor or outdoor unit
• When it started (suddenly, gradually)
• What fan setting it’s loudest at

We’ll come back with a likely diagnosis and a slot offer.