Furnace Troubleshooting 101: What’s That Noise?

When it comes to machinery and mechanical equipment, hearing a peculiar noise can be a cause of concern for the untrained ear. You may have heard your furnace make a humming sound but had no clue what to tell the HVAC specialist when you called them—only to find out that the noise was normal after all. 

Knowing what problems are associated with specific sounds you’re hearing is crucial in making your furnace repair or replacement as smooth as possible. Here are some explanations as to why your furnace is making a particular noise:

Noises that a normal furnace makes

There are several sounds that your furnace can make that you shouldn’t be worried about. For instance, furnaces that start to run a heating cycle will naturally make some noise after being switched on. These are often little pops or clicks upon starting that settles into a low hum as it keeps running. You can compare it to the click and low noise of a gas stove and its flame. As long as the noise isn’t disruptive in your home, there doesn’t appear to be any problem.

Noises that you should watch out for

The furnace will sometimes emit unfamiliar noises that can be alarming. Here’s a guide to the most common sounds to watch out for:

Scraping or grinding

This usually indicates dry bearings in the furnace’s blower motor that need to be lubricated.

Loud humming sound

While a low hum is normal for a running furnace, a loud hum could mean an issue with the capacitor or the fan. 

Constant clicking

Although normal when heat cycles start and stop, repeated clicking during a heating cycle is due to a faulty compressor or control panel issues. 


Rumbling noises that can be heard through the house need immediate attention since this could indicate a serious problem: fuel may be burning in the combustion chamber even though the burners have shut down. Immediate action is required in this case because there is a risk of carbon monoxide poisoning. 

Loud banging and popping noises

Another sound indicative of a serious issue with your furnace is a loud popping and banging. This happens when warm air comes into contact with the cold metal. 

If the popping is loud, then it means the gas furnace’s burners are dirty. Gas accumulation occurs as a result, and the heat exchanger could crack. This is very dangerous and calls for immediate furnace repair


If you hear thumping sounds, it usually means that the blower wheel or motor is unbalanced. This requires immediate attention from an HVAC specialist. 

What to do with your furnace

One of the best things you can do is to schedule preventive maintenance before hearing any of these noises. Furnace maintenance can prevent any of the dangerous issues above, and you can be assured that your furnace is in tip-top shape.

However, if you already hear some of these noises, it might be time for repair or replacement. Furnace replacement services can determine the issue and, depending on the severity, determine if your furnace is dying and needs to be replaced completely.


Knowing the various sounds that a furnace makes, both normal and dangerous, will allow you to determine how urgent the problem is. Being equipped with this knowledge makes it easier for the HVAC technician you call to determine what repairs are needed before making the trip. Trusting your ears can help save your furnace and your home a lot of trouble!

Furnace maintenance is necessary to keep it running safely and smoothly. Here at Legacy, we are heating and cooling experts that resolve various furnace and air conditioner related problems on a daily basis. We offer various heating and cooling solutions to get your systems up and running without a hitch. To learn more about our services, contact us today!

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