# Furnace making noise: banging, squealing or rattling

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

## Short answer

Ticks and pops from the ducts as they warm up are normal. A whistle usually means a clogged filter or closed vents, and a rattle can be something touching the furnace. A loud boom when it lights, a squeal, grinding or scraping are not normal: turn the furnace off at its switch and call a technician.

> Safety first: A loud bang or boom when the furnace starts can mean gas builds up before it lights. Turn the furnace off and call. If you smell gas, do not touch switches: get out and call 911 or your gas company from outside.

## How to tell which furnace noises need a pro

![Cartoon furnace in a closet shaking and banging, with a broom leaning on it](https://pros411.com/img/guias/furnace-making-noise.webp)

1. **Bangs, squeals or rattles from the furnace.** Every furnace makes some noise. The trick is telling a normal tick from a sound that needs a technician.
2. **Whistling? Replace the filter.** A clogged filter makes the blower pull hard and whistle. Put in a new one of the same size and open any closed vents.
3. **Rattling? Clear things away from it.** A broom, a box or a shelf touching the furnace rattles with the blower. Move them away and keep three feet clear.
4. **Ticks and pops from the ducts are normal.** Metal ducts tick and pop as they warm up and cool down. You hear it most when a cycle starts and ends.
5. **Boom, squeal or grinding? Off, then call.** A boom when it lights, a squeal, grinding or scraping metal mean a part is failing. Turn the furnace switch off and call a technician.

## What the noise usually means

- Boom or bang when it starts: delayed ignition, the gas lights late. Turn it off and call.
- Squealing or screeching: the blower motor or its bearings, or a worn belt on older furnaces.
- Grinding or scraping metal: the blower wheel or the motor bearings. Turn it off.
- Rattling from inside the cabinet: a loose part or the inducer motor.
- Humming or buzzing: a motor, a capacitor or the transformer.
- Clicking over and over without lighting: the ignition is failing.

## What not to do

- Do not open the panels to look for the noise while the furnace has power.
- Do not oil motors or tighten parts inside the cabinet.
- Do not ignore a boom at startup. Over time it can crack the heat exchanger, which can leak carbon monoxide.

## When to call an HVAC technician

- It makes a boom or a bang when it lights.
- You hear squealing, grinding, scraping or a loud hum.
- The rattle comes from inside the cabinet.
- A new noise comes with a burning smell or soot around the furnace.

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## Frequently asked questions

### Why does my furnace bang when it turns on?

A loud bang right when it lights is often delayed ignition: gas builds up for a moment before it catches. Turn the furnace off and call a technician. Softer pops from the ducts as they warm up are normal.

### Is it normal for a furnace to make noise?

Some noise is normal: a click when it starts, the hum of the blower, ticks from the ducts. Booms, squeals, grinding and loud rattles are not.

### Why is my furnace squealing?

Usually the blower motor or its bearings, or a worn belt on older furnaces. Turn it off and call a technician before the motor fails.

### Why does my furnace rattle?

Often something touching the cabinet or a loose outer panel. If the rattle comes from inside, have a technician check the motors and the heat exchanger.

### Can a dirty filter make my furnace noisy?

Yes. A clogged filter makes the blower strain and can cause a whistle. Replace it and the noise often goes away.