Aircon Making Noise? Causes & How to Fix Loud AC Sounds

Understanding Aircon Noises

Your aircon should operate quietly — a gentle hum is normal, but rattling, buzzing, hissing, or clicking sounds indicate something needs attention. Different noises point to different problems, and identifying the type of sound helps us diagnose the issue faster.

Types of Aircon Noises and Their Causes

Rattling or Vibrating

What it sounds like: Loose, metallic rattling or vibrating sound, often intermittent.

Common causes:

• Loose fan blades — The fan blade has loosened from the motor shaft
• Dislodged panel — The front cover or side panel has come loose
• Debris inside the unit — Small objects or broken parts rattling around
• Loose mounting brackets — The unit’s wall brackets have loosened over time
• Loose outdoor unit — Compressor vibration amplified by loose screws

Severity: Usually not urgent, but should be addressed to prevent further damage.

Buzzing or Humming

What it sounds like: Continuous electrical buzzing or loud humming sound.

Common causes:

• Failing fan motor — Worn bearings creating electrical resistance
• Compressor issues — The outdoor unit’s compressor struggling to start
• Loose wiring — Electrical connections vibrating under load
• Capacitor failing — The start/run capacitor losing capacity
• Frozen evaporator — Restricted airflow causing abnormal operation

Severity: Moderate — a failing fan motor or capacitor will get worse over time.

Hissing

What it sounds like: Steady or intermittent hissing, like air escaping.

Common causes:

• Refrigerant leak — Gas escaping from a cracked pipe or loose connection
• Expansion valve operation — Normal in some models when the refrigerant changes pressure
• Internal valve issue — Faulty reversing valve (in reverse-cycle models)

Severity: If it’s a refrigerant leak, address it promptly. A leak means declining cooling performance and higher electricity bills.

Clicking

What it sounds like: Repetitive clicking, either regular or random.

Common causes:

• Normal relay operation — A single click at startup/shutdown is fine
• Faulty thermostat — Constantly engaging and disengaging the compressor
• Defective relay — The starter relay failing to engage properly
• PCB board issue — Electronic control board malfunction

Severity: Repeated or continuous clicking needs professional diagnosis. If your unit is also displaying a blinking light or error code, check our aircon error codes guide to help identify the issue.

Squealing or Screeching

What it sounds like: High-pitched squealing or screeching, usually from the indoor unit.

Common causes:

• Worn fan belt (older models)
• Dry bearings — The blower motor bearings need lubrication or replacement
• Misaligned blower wheel — The fan wheel rubbing against the housing

Severity: Address promptly — worn bearings can seize and cause the motor to fail.

What to Do About a Noisy Aircon

Quick Checks You Can Try

1. Check the front panel — Make sure it’s properly clipped in place
2. Check for objects — Remove anything placed on top of or near the unit
3. Clean the filters — Dirty filters can cause whistling or abnormal sounds
4. Listen to the outdoor unit — If the noise comes from outside, check for debris around the unit

When to Call a Professional

• The noise is getting louder over time
• You hear hissing (possible refrigerant leak)
• The noise is accompanied by reduced cooling
• Clicking is continuous or repetitive
• You hear grinding or screeching sounds

Our Troubleshooting Pricing

Book Your Noise Diagnosis

WhatsApp us at +65 9427 3833 and describe the sound. If possible, send a short video — this helps our technician prepare for the visit and arrive with the right parts.