HomeAnswersFurnace noises and what they usually mean
Furnace noises and what they usually mean
Banging or booming on startup
Usually delayed ignition: gas builds up before it lights. Worth a visit. It is hard on the heat exchanger and it is not a sound to wait out.
Rumbling or low booming while running
Often a dirty burner, a gas pressure problem, or oil-canning in the ductwork as it heats. Duct noise is harmless; burner noise is not. A technician can tell the two apart in minutes.
Whistling
Almost always a restriction: a loaded filter, a blocked return, or undersized duct. Start by checking the filter and clearing the return grille.
Screeching or squealing
A blower bearing or belt on its way out. It usually gets worse quickly, and it is cheaper to fix before the motor seizes.
Ticking or clicking after shutdown
Normal on most furnaces: metal cooling down, or a relay cycling. It matters only if it happens during the run cycle rather than after it.
One noise that is always urgent
Any rattle that started after a repair, or a sound paired with a gas smell. Those two go straight to a call, not a checklist.