Key takeaways
- Banging or clanking usually means a loose or broken part in the compressor or fan.
- Hissing often points to a refrigerant leak, which needs a professional.
- Screeching can be a failing fan motor or belt.
- A new or sudden loud noise is worth checking before it becomes a bigger repair.
A healthy AC makes a steady, low hum. When a new sound shows up, your system is usually trying to tell you something. Here is how to translate the most common AC noises, and how urgent each one is.
Quick answer
Humming is usually normal. Buzzing can be electrical. Banging or clanking means a loose part. Hissing suggests a refrigerant leak. Screeching points to a motor or belt. Any loud, sudden, or grinding noise is worth a professional look before it worsens.
Banging or clanking
This often means a loose or broken component inside the compressor, or a loose fan blade hitting something. Continuing to run the unit can cause more damage.
What to do: turn it off and call a technician to inspect the compressor and fan assembly.
Hissing or bubbling
A hiss frequently indicates refrigerant escaping from a leak. Besides poor cooling, low refrigerant can damage the compressor, which is the most expensive part to replace.
What to do: this requires a certified technician to find the leak, repair it, and recharge the system.
Screeching or squealing
High-pitched screeching usually comes from a failing fan motor, a bad bearing, or a worn belt on older units. It tends to get worse over time.
What to do: schedule service before the motor fails entirely on a hot day.
Buzzing or rattling
Buzzing can be an electrical issue such as a failing capacitor or contactor, while rattling is often loose hardware or debris in the outdoor unit. If your AC also struggles to start, see our guide to an AC that won't cool.
What to do: clear visible debris from the outdoor unit; if buzzing continues, have the electrical components checked.
Hearing something new?
Don't wait for a breakdown. We will diagnose the sound and fix it before it gets worse.
