Furnace Making Loud Noise

A boom at ignition or a shriek from the blower says a part is working under stress, and catching it early beats replacing what it breaks.

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When this becomes an emergency

A dull boom shakes the ductwork the moment the burner catches.
A metallic shriek rises out of the blower compartment during operation.
Something is knocking inside the cabinet and getting worse by the day.
The system is plainly louder now than it was last season.

What a pro does

Furnace noises fall into a few distinct families, and the sound itself narrows the search. A boom at startup usually means gas pooled in the chamber before it lit, which hammers the heat exchanger a little harder every cycle and deserves attention now rather than in spring. A shriek or grind almost always comes from blower bearings or belt tension, isolated by listening at each component while it runs. Loose cabinet panels and duct joints buzz loudly for a very small reason, so that's ruled out early.

Frequently asked questions

How dangerous is a boom at startup?

Delayed ignition is a real concern. Repeated over a season it can stress a heat exchanger toward cracking, which turns a noise complaint into a combustion safety issue.

Could the wind be making the noise instead of the furnace?

Sometimes. A gusty night can set a poorly capped flue or a loose vent hood chattering, and that sound travels down through the ducts convincingly.

Does a squeal always mean the motor is done?

No. A dry bearing or a slack belt makes a similar sound, and the fix for those is not the same as replacing a motor.

Can the furnace keep running until someone looks at it?

Running it long enough to describe the sound accurately is fine, but grinding and banging are not sounds to live with for a week.

Furnace Making Loud Noise?

Get connected with a local pro now.

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