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Green Bay Heating
Heating · Wisconsin

Furnace Making Loud Noise

A new bang at ignition or metal-on-metal scraping means a part is working under stress it was never meant to carry, so get it looked at before it lets go.

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When this becomes an emergency

What a pro does

Diagnosing noise means being there when it happens. A tech runs the unit and isolates the sound by location and by timing within the cycle, since a rumble at ignition and a whine at shutdown come from opposite ends of the machine. Delayed ignition produces that startup thump: gas collects a moment too long before the flame catches, and the small explosion that follows punishes the heat exchanger. Dirty burners, a lazy ignitor, or a drafty flue can all cause it. Bearing noise doesn't behave that way. It builds slowly, tracks with blower speed, and often precedes a motor failure by weeks. Loose sheet metal's the cheerful outcome, and it happens plenty in older houses where a converted duct trunk hangs off joists and buzzes at one particular fan speed. Rattling that changes when you press a panel is telling you where to look.

Frequently asked questions

Worried enough to have it seen soon. Each one is a small pressure event inside the heat exchanger, and repeated over a season it can open a crack that turns a noise problem into a combustion safety problem.
Cold changes draft and it makes metal contract, so both combustion behavior and duct expansion noise get louder. A marginal fault often stays quiet until conditions push it over the line.
A faint hum from a transformer is normal. A loud hum with no motion usually means something is energized and trying to start without succeeding, and that is worth shutting off at the breaker.
Often yes. Oil-canning trunk lines, unsupported runs, and undersized returns are the usual culprits, and correcting airflow or adding support addresses the sound at its source.

Furnace Making Loud Noise?

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