A noisy furnace heater fan could be indicative of a serious problem, such as imminent failure of a fan motor. Most noisy heater fans can be quieted with a simple repair. The type of noise your noisy heater fan is making may be a clue to what is wrong and how to fix it. Heater fans may squeak, click, buzz or make a whining sound when starting up. If the sound persists after minor repairs are attempted, call a professional to fix your furnace fan.
Repair a squealing sound by adjusting the belt. A heater fan belt will squeal when it is misaligned or worn. Turn off the electricity to the furnace. Remove the access panel with a screwdriver. Replace the worn belt, or realign the belt properly.
Tighten the transformer if the furnace fan makes a humming or a buzz sound after the fan goes off. Turn off the electricity; remove the access panel, and tighten the screws that hold the transformer in place. If there is a space between the transformer and the wall, the transformer will vibrate and make noise.
Tighten the screws on all access panels with a screwdriver. Most rattling noises are a result of loose access panels. Tightening the screws can often reduce or eliminate this noise.
Call a furnace service technician if your furnace makes a ticking sound after the fan goes off or if the furnace whines during operation. In a gas furnace, a ticking noise may indicate that there is a gas leak and a whine indicates that there is an air leak. Only a professional furnace technician should attempt to repair a furnace gas leak.