Write down when the noise happens: the moment heat starts, the whole time the blower runs, or only at the outdoor unit. A light tick as metal warms up can be ordinary. A bang when the burners light is not. Delayed ignition, gas that pools and then lights, is a reason to shut the furnace off and have it checked. Do not keep cycling it to “see if it does it again.”
A whistle that tracks the blower is often a packed filter, a closed register, or a return that cannot move air. That is airflow, and it belongs with the filter before it belongs with a new blower. A screech or a squeal can be a blower motor or, on an older furnace, a belt. A click at the outdoor heat pump can be the contactor pulling in, which is normal once per start, not a buzz that continues the whole cycle.
A rotten-egg smell overrides the noise. Leave, do not use switches, and call 911 or Southwest Gas. Burning-dust smell on a successful first fire is heater smells burning. Rattling ducts that pop when the blower starts are ductwork, not an igniter.
Symptoms and how they’re checked
No price column. The noise names the check. It does not name a part price.
| Noise | Likely cause | How it’s checked |
|---|---|---|
| A bang when the burners light | Delayed ignition | Shut it off. The ignition sequence is checked. Do not keep restarting it. |
| A whistle the whole time the blower runs | Filter, a blocked return, or too many closed registers | Filter and returns before the blower is condemned. |
| A pop from the ceiling when the blower starts | Ducts expanding or a loose connection | Whether the pop is at the vents, not in the furnace cabinet. |
| A squeal or screech from the furnace cabinet | Blower motor or, on an older furnace, a belt | The noise has to be tied to the blower running, not to the burners. |
| One click at the outdoor unit, then it runs | Contactor pulling in | Often normal. A buzz that continues is a different check of that contactor. |
| Rumbling after the burners shut off | Air in the heat exchanger as it cools, or a burner issue | When it happens in the cycle. A continuing rumble with a smell is not “just cooling metal.” |
Name, mobile phone, and ZIP are required. Street address can wait. We follow up the same business day by phone or email. That is a callback, not a promise of a repair the same day.