# AC making loud noises: buzzing, banging, squealing

Updated: 2026-10-24 · https://pros411.com/en/guides/hvac/ac-making-noise

## Short answer

Turn the AC off at the thermostat if the noise is loud or new, so a loose part does not do more damage. Buzzing usually points to an electrical part, banging or clanking to a loose or broken part, and squealing to a fan motor or belt. With the power off at the disconnect box, lift sticks and leaves off the top of the outdoor unit. If the noise comes back, call a technician.

> Safety first: Never reach into the fan or open the panels of the outdoor unit: parts inside can hold an electrical charge even with the power off. Switch the disconnect box to "Off" before you clear anything from the unit.

## What to do when your AC makes a loud noise

![Cartoon outdoor AC unit shaking and making buzzing, banging and squealing noises](https://pros411.com/img/guias/ac-making-noise.webp)

1. **A new, loud noise.** Buzzing, banging, squealing or rattling from the outdoor unit. A new noise means something changed, so act early.
2. **Turn it off at the thermostat.** Set it to "Off" so a loose part does not break more. Remember how it sounded so you can describe it.
3. **What the sound tells you.** Buzzing: usually an electrical part. Banging or clanking: a loose or broken part. Squealing: a fan motor or belt. Hissing: a possible refrigerant leak.
4. **Power off, lift debris off the top.** Switch the disconnect box to "Off". Lift sticks and leaves off the top grille. Never reach inside the fan.
5. **Power on and listen.** Turn the disconnect back on and set the thermostat to "Cool". A rattle from a stick may be gone. Buzzing or banging again? Leave it off and call.

## Sounds and what they usually mean

- Buzzing or humming with the fan stopped: often a failed capacitor or contactor.
- Banging or clanking: a loose or broken part, like a fan blade or a part inside the compressor.
- Squealing or screeching: a worn fan motor bearing, or a belt on some older indoor units.
- Rattling: loose screws or panels, or debris in the unit.
- Hissing or bubbling: a possible refrigerant leak.
- A click when it starts or stops is normal. Constant clicking is not.

## What not to do

- Do not push a stick or a screwdriver into the fan to stop a noise or to get it spinning.
- Do not open the outdoor unit. The capacitor inside can hold a charge even with the power off.
- Do not keep running an AC that bangs or screeches. A small repair can turn into a new compressor.

## When to call an HVAC technician

- Buzzing, banging or screeching comes back after you clear the top of the unit.
- It hums but the fan does not spin.
- You hear hissing or bubbling near the lines.
- The unit shakes, or you smell burning.

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## Frequently asked questions

### Why is my AC making a loud buzzing noise?

Buzzing usually comes from an electrical part, like a failing capacitor, a contactor or a loose wire. Turn it off and call a technician, since those parts can hold a charge.

### Why is my AC making a banging noise?

Banging or clanking usually means a loose or broken part, such as a fan blade or a part inside the compressor. Turn it off right away to avoid more damage.

### Why is my AC squealing?

Squealing often comes from a worn fan motor bearing or, on some indoor units, a belt. A technician can replace the motor or the belt before it fails.

### Is it normal for an AC to make noise?

A steady hum from the fan and compressor and a click when it starts or stops are normal. New loud noises, rattles or squeals are not.

### Should I turn off my AC if it is making a loud noise?

Yes. Set the thermostat to "Off" and call a technician, especially for banging, screeching or buzzing. Running it can make the damage worse.