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My Furnace Is Making Weird Noises! What’s Wrong?

surprised-by-loud-soundAlthough odd noises coming from your furnace may be annoying, there is a good reason to be thankful for them: they can warn you when something is wrong that needs the help of HVAC professionals to correct. Furnaces aren’t yet advanced enough where they can automatically determine what their malfunctions are and communicate the data to their owners. Maybe someday we’ll have that technology. For right now, you’ll have to settle for paying attention to warning noises so you know to call us for furnace service in Wesley Chapel, FL.

Anyway, let’s look into what these sounds might mean…


A high-pitched mechanical shrieking often means there are problems with the bearings in the blower fan motor. The bearings may have dirt in them or they are wearing down. If the bearings fail, it will soon cause the motor to burnout. You want the bearings cleaned or replaced before this happens, so don’t delay calling for repairs.


This grinding sound, like a dying car motor, is probably a dying blower motor. The motor is likely burning out, and you may also detect an acrid odor coming through the vents. Shut the furnace down and call for repairs. The motor will probably need to be replaced. 


Nope, a furnace shouldn’t whistle as it works. If it is, it usually indicates a blockage to the airflow through the system. A common cause for this is an excessively clogged furnace filter. Check if the filter needs to be changed (it usually should be swapped out every 1 to 3 months) and put in a new one if it’s clogged.


This is a normal sound during the start of a heating cycle in a gas furnace. However, if you start to hear it often, or it becomes louder than before, it points toward a wide range of potential problems. It could be dirt or grime on the burners, stuck gas valves, loose electrical connections, a failing ignition system, or even cracks developing on the heat exchanger. Don’t take risks with this noise: shut the furnace down at the furnace switch and call for repairs.


This is a surprising sound from a furnace, a sudden loud whoosh noise during the startup cycle. What you’re hearing is a large amount of unburned combustion gas igniting at once. This shouldn’t happen: it means too much gas is collecting before it ignites, indicating trouble with the ignition system, a failure with the flame sensor, or burner problems.


Sometimes this is the simplest problem to fix—just check the panel to the furnace to make sure it’s securely shut. If the noise continues, it probably means there are loose parts in the furnace that are becoming looser from vibrations. It could also be loose parts in the blower assembly. 

Metal-on-Metal Clanging

The sharp sound of metal striking metal probably comes from the blower fan. It could be coming loose, a bent blade is striking the casing, or a large part is loose in the assembly. No matter what the source of the sound is, parts of the furnace are suffering from damage, so shut the system off and have it looked into right away.

Experience the Balanced Air, Inc. Difference! We have served the Tampa Bay Area since 1988. 

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