Why Is My Furnace Making a Buzzing Noise?

Humming, buzzing, screeching, and banging - oh my! The older your furnace gets, the more likely it is to start making noise. Learn about what these furnace noises mean and what you can do about them. 

Spoiler alert: if your furnace is making loud noises or strange sounds, the fix may not be as simple as checking the thermostat or changing the filter. Make plans now to call an HVAC professional. 

Keep reading to see what might be causing these sounds.

If your furnace is making a humming noise or humming sound, rest assured, that’s normal. Once your furnace ignites, the furnace humming sound is a signal that things are going smoothly.

Other normal sounds include a clicking noise before ignition. In addition, you might hear a slight pinging or popping from your ductwork as it expands when the heat first comes on.

If your furnace is making a buzzing noise, that’s not a normal sound. Buzzing is louder than the everyday humming. There can be several causes. Let’s take a look. 

A common reason for furnace buzzing is a loose transformer box. A furnace transformer regulates the incoming voltage to an appropriate voltage for the furnace to use. This is more common after a new installation. With an older furnace, the transformer may be malfunctioning and needs to be replaced.

A furnace making a buzzing sound may also be due to a faulty furnace capacitor. Furnace capacitors help regulate the power of furnace motors such as the blower motor. A failing or bad capacitor can cause a buzzing noise, more commonly in older furnaces. Call for furnace repair. 

The blower motor works hard. It runs all winter when the furnace is running and runs in the warmer months as well, circulating cool air from your air conditioner or heat pump. An old or poorly maintained blower motor can cause a buzzing sound as well as other noises. Call for furnace repair.

Another HVAC issue that can cause buzzing isn’t the furnace at all. Different than the normal pinging or popping, ductwork that causes a buzzing or vibrating sound indicates loose connections. While not an emergency, Loose and leaky ductwork can cause uneven heating and cooling, energy loss, and higher utility bills. Consult with your HVAC professional to see if duct sealing will fix the problem.

A sudden bang at the furnace when it first starts up could indicate a delayed gas ignition issue, and needs immediate attention. What sounds like banging or clanging coming from the registers is just the noise your ducts make as they adjust to temperature changes.

A high-pitched squealing or screeching coming from your furnace is likely a sign of trouble with the blower motor. Over time, the ball bearings in an older furnace’s furnace fan motor may start to wear out. Call for furnace repair. The HVAC technician may be able to solve the problem by replacing the ball bearings and lubricating the motor, but you may need a furnace blower motor replacement.

If when your furnace starts it makes a loud rumbling sound, it could be due to dirty gas burners. Make sure to get them cleaned as part of regular maintenance. A furnace can also sound like it’s rumbling if you’re in the room directly above the furnace and it’s running full-blast. 

A whistling sound when your furnace is running most likely points to airflow problems. Check your furnace filter and change it if it’s dirty. Make sure the registers are open and the return air vents are not covered or blocked by furniture.

In addition to changing your air filter regularly, the best thing you can do for your furnace is to schedule an annual furnace tune-up. During this visit, an HVAC technician will inspect your furnace, check electrical and mechanical components, clean and lubricate, run safety checks, and more. 

A regular tune-up of your heating system can help eliminate those pesky noises coming from your furnace, and keep an aging furnace functioning. Starting early with yearly maintenance can help prolong the life of a new furnace, as well. Consider setting up a maintenance plan with your local HVAC company to keep your system running at peak performance.

Opt into Trane Diagnostics for peace of mind. Through the Trane Home App, you can give your dealer remote monitoring capabilities. Your Trane smart thermostat sends data in real-time to your dealer, alerting them to any issues, sometimes before you even realize there’s a problem. 

They can run furnace troubleshooting tests to pinpoint the problem. In some cases, they may be able to solve the problem remotely. In this situation, you would grant them one-time dealer remote access (DRA). 

If they need to schedule an on-site service call, the technician will arrive with the knowledge gained from remote access. This enables shorter service calls and ensures the technician has the proper replacement parts. 

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

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