What's That Sound? Identifying Furnace Noises

Posted on: 29 December 2014

Your home's furnace is normally considered a silent partner when it comes to heating your home. However, it can make itself heard whenever it needs attention. If you're concerned with the noises coming from your furnace, you can use this guide to identify and diagnose them on your own. Then you can decide if you need an experienced HVAC technician from a place like HomeSmart From Xcel Energy to evaluate your furnace's health.

Pinging and Popping Sounds

You may occasionally hear pinging and popping noises coming from the ducts after the furnace has been operating in heating mode. Those noises you're hearing are the result of the metal ductwork contracting in very small increments as it cools down. These pinging and crackling noises are perfectly normal and nothing to worry about.

You may also hear popping noises shortly after having your ductwork cleaned. Drastic changes in static air pressure are usually responsible for these noises. Removing large amounts of dust and debris from the ducts can actually increase the overall volume of air that passes through the ducts, causing the ducts to expand outward by a small degree in response to the increased air pressure.

Booming Sounds

If you hear what sounds like a miniature explosion shortly after turning on your furnace, it may be due to delayed ignition. This usually happens when the gas valve opens and delivers gas to the burners, but the burners fail to ignite immediately due to a number of issues, including clogs caused by dirt or rust accumulation. Gas continues to build up in the furnace until the burners finally ignite, causing that characteristic detonation noise.

But delayed ignition isn't the only problem that can create a booming noise in your furnace. A sudden increase in static pressure can also cause the metal ducts to suddenly expand. When that happens, you'll hear that characteristic "boom" when you start your furnace.

If you're having trouble pin-pointing the noise, here's something to keep in mind:

  • If you hear a "bang" or "boom" at the furnace, it's likely the burners.
  • If the "bang" or "boom" noise sounds like it's happening several feet away from the furnace, then it's likely the ducts.


Rumbling, buzzing and other vibrating noises can set any homeowner on edge after a while. To solve this problem, you may want to take a close look at your furnace's blower fan motor. Any of the following could be responsible for causing your vibration problem:

  • Loose or deteriorated fan motor mounts
  • Unbalanced fan shaft
  • Worn-out bearings
  • Fan coming into contact with the fan housing

You may also want to take a look at your draft inducer motor, as it can produce a rumbling noise as well as vibration if it needs cleaning or servicing. It's a good idea to have your HVAC technician take a look at these issues and make the necessary repairs and adjustments.

Screeching Sounds

If grinding or screeching noises are driving you up the wall, the following causes may be to blame:

  • Worn-out fan motor belt
  • Bad fan motor bushings or bearings
  • Lack of proper lubrication

Simply lubricating the fan motor shaft and bushings usually solves the screeching problem on a short-term basis. However, you'll want to invest in a new blower fan motor in the future. If the cause of the noise is limited to just the fan belt, then you won't have to worry about replacing your motor.

Whistling Sounds

Those annoying whistling sounds could be the result of a vent register that's loose or improperly sealed against the wall and the duct it's attached to. Look for any loose mountings or screws and tighten them up. You may also have to apply caulk around the vent register to seal up any gaps found between the register and the wall.

If that doesn't help, your last option is to run the furnace fan at a slightly lower setting, which reduces the amount of air pressure in the ducts. This may not be feasible if you have a single-speed furnace.