Glendale Heating & Air Conditioning | Serving Greater Seattle Since 1938

After years in your home, you may become immune to your house’s sounds: the chug of the laundry machine or the drone of the shower, for example. So when you hear the hum of your HVAC’s blower or the occasional bang of the furnace, it doesn’t trouble you.

However, there remain some HVAC-related sounds you shouldn’t ignore. You might notice an unexpected screech or a startling boom. While you could put these sounds out of your mind, this decision could cost you in the long run. A small problem can evolve to a bigger and more expensive issue over time.

If you hear sounds that seem louder or more frequent than typical, read through the following information to help you identify the problem’s source. You’ll then feel prepared to speak with an HVAC specialist and resolve the issue sooner. However, you first want to acquaint yourself with the basic HVAC components to help you diagnose these noises.

HVAC Basics

A basic overview of an HVAC system is quite simple. Cool air comes back into the system through a return register and return duct. There, filters remove dust and debris to keep the air clean. The air then moves to the furnace, and the heat exchanger warms the air. Once the air reaches the desired temperature, the blower sends this air down the supply duct and through supply registers back into your home.

The sounds you hear could come from the furnace itself or ducts, so try to identify the location of the noise as you diagnose the problem.

Noisy Draft Inducer

A draft inducer (or vent blower) is the most common problem on a gas furnace or boiler to cause a noticeable noise. It’s the first sequence of events upon a call for heat, and it runs through most of the heating cycle.

Once the vent is moved through the pressure switch, the system comes on and starts heating. The small motor mounted within the housing can begin to make noise when there is buildup on the wheel (such as sulfur or creosote) or when the motor is close to the end of its usable life. The remedy for a noisy inducer is to replace the entire assembly.


If you have metal ductwork, remember that it expands and contracts as the system turns on and off. Sounds could come from the ductwork itself or even from the hardware that holds the system together. Insert bits of foam or rubber in especially troublesome areas to reduce the noise, or try insulating the system to further reduce the volume.


A metal scraping sound indicates a loose or broken part. The blower wheel could simply have come loose from the motor shaft and now hits the casing as it runs. In this situation, a professional simply needs to tighten the wheel.

The sound could also come from something more serious, such as a broken blower wheel or motor mount. These issues both require replacement.

Regardless of the sound’s origin, turn off the furnace and contact a professional.


You might hear a rumbling, rattling, or flapping noise coming from your ducts. This likely results from items in the registers, especially if your vents are on the floor. Small toys, writing utensils, screws, or nails could fall into the register and jostle as you turn the HVAC system on.

If you can remove the register yourself, simply pull out any misplaced items inside of it. For a more thorough cleaning, call a professional to eliminate all noisy debris.


If you hear a bang when you first turn on the heat, it could be a duct issue. Again, this could come from metal ducts that contract and expand. If the ducts fit poorly or have flimsy material, they may make sounds as the system turns on and off. You can also look for airflow issues that come from filtration problems or closed vents. Try replacing the air filters and opening any closed registers.

A bang, pop, or boom could also indicate a larger issue. If your system has accumulated dirt, the sound might result in an ignition delay. A dirty burner, faulty pilot light, or burner assembly issue can cause the furnace to ignite slower than usual. While the pilot light takes more time to ignite, gas gathers. When the furnace finally does light, the accumulated gas results in a small explosion. Over time, this process can damage your heat exchanger — an expensive part to replace.

If you hear these sounds, you can best protect your HVAC system with a call to a professional. He or she can confirm any theoretical diagnosis and resolve the issue.

Once you have a functioning furnace again, remember that regular maintenance helps keep your furnace quiet. A professional can remove excess debris, replace loose or faulty parts, including belts and motors, and lubricate the system. Annual maintenance also helps your system last longer so you can save money long-term.

Work with an HVAC professional today and in the future to eliminate any strange noises and maintain your system for years to come.

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