Air Conditioner Making Noise? Common Causes & Fixes
- Apr 16, 2026
- Troubleshooting
Is Your Air Conditioner Making Strange Noises?
Air conditioners aren’t silent, but they should run with a consistent, quiet hum. If your AC starts making unusual noises — banging, rattling, squealing, or buzzing — it’s telling you something needs attention. Here’s what each noise means and what to do about it.
Rattling or Vibrating
What it sounds like: Loose, shaky noise from the indoor or outdoor unit.
Common causes:
- Loose screws or panels on the unit casing
- Debris (leaves, sticks) inside the outdoor unit
- Loose fan blade or worn fan motor mount
- Outdoor unit not level on its mounting pad
What to do: Check for visible loose panels and tighten any accessible screws. Clear debris from around the outdoor unit. If the rattling persists, the fan motor mounts may be worn and need professional replacement.
Banging or Clanking
What it sounds like: Loud, repetitive banging from the outdoor unit.
Common causes:
- Broken or disconnected fan blade hitting other components
- Failed compressor internal components
- Loose connecting rod or piston pin in the compressor
What to do: Turn off the system immediately. Banging usually indicates a serious internal fault — a broken fan blade can cause significant damage if left running, and compressor issues require professional diagnosis. Call a technician.
Squealing or Screeching
What it sounds like: High-pitched squeal at startup or during operation.
Common causes:
- Worn fan belt (older ducted systems)
- Dry or failing fan motor bearings
- High internal pressure in the refrigerant system
- Misaligned fan blade rubbing against the housing
What to do: A brief squeal at startup in cool weather can be normal as the compressor pressures equalise. If squealing is persistent or gets worse, turn off the unit and book a service — worn bearings or high pressure need professional attention.
Buzzing
What it sounds like: Constant electrical buzzing from the outdoor unit.
Common causes:
- Failing contactor relay (the electrical switch that starts the compressor)
- Loose electrical connections
- Refrigerant leak causing the system to struggle
- Debris interfering with the condenser fan
What to do: Electrical buzzing should always be checked by a qualified technician. Loose connections can be a fire hazard, and a failing contactor can damage the compressor. Don’t ignore persistent buzzing.
Hissing or Gurgling
What it sounds like: Hissing, bubbling, or gurgling from the indoor unit or refrigerant lines.
Common causes:
- Refrigerant leak — gas escaping through a crack in the copper piping
- Normal refrigerant flow during startup or shutdown (brief gurgling is OK)
- Blocked condensate drain causing water to back up
What to do: Brief gurgling at startup is normal. Continuous hissing suggests a refrigerant leak which needs professional repair — running a system low on gas damages the compressor and reduces cooling capacity significantly.
Clicking
What it sounds like: Repeated clicking from the outdoor unit, especially at startup.
Common causes:
- Failing thermostat or control board
- Defective relay switch
- Electrical issue preventing the compressor from starting
What to do: If the unit clicks but doesn’t start, the compressor may be struggling against a faulty component. This needs professional diagnosis — repeated failed starts can damage the compressor.
When to Call a Professional
Call a technician if:
- The noise is new and getting worse
- The unit isn’t cooling or heating properly alongside the noise
- You hear banging, screeching, or continuous hissing
- The outdoor unit is buzzing but not running
- You notice any burning smell accompanying the noise
Sun City Air diagnoses and repairs all air conditioner noise issues across Brisbane. Same-day service available.
Call Sun City Air on 07 3283 5566 or book a repair online.
More troubleshooting: AC not cooling guide | AC repair services | Emergency repairs
