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Reasons Your Furnace Makes a Loud Noise | Mission Air Conditioning

February 23, 2017 | Blog

Why Is My Furnace Making a Loud Noise?

Usually, homeowners don’t give their HVAC system, much thought as long as it’s working correctly. It’s not until banging or another loud noise is coming from the vicinity of the HVAC system that you start to pay attention. At Mission Air Conditioning, we want to not only offer professional heating repair in Houston but also educate our customers on their HVAC system. Let’s take a moment to discuss why your furnace makes loud noises.

Vibrating and Rattling

If you hear rattling or vibrating coming from either your ducts or the furnace itself, you can easily take care of the problem yourself, no professionals required. First, you’ll want to inspect your ducts to see if they’re loose, tightening or adding screws as necessary. You can also use duct tape to keep ducts from rattling loose. There’s a chance you might need to add cork or rubber pads underneath your furnace to keep it level.


The sound of whistling coming from your furnace might indicate there’s a gap in your ducts or too much air pressure. Before remedying the situation, try your best to determine exactly where the noise is coming from. The reason for the whistling sound could be that your furnace filter has become clogged, too. Pull out your filter and listen to see if the noise stops after doing so to determine for sure whether the cause is a clogged filter. If it’s time to replace or clean your filter, it might also be time for heating repair, so be sure to get a tune-up.

Banging When the Furnace First Turns On

When you turn your furnace on and hear banging, there are two potential problems. The first is that the structure of your ducts is compromised. It needs a piece of metal that’s a bit thicker than the ducts to be screwed across and onto the part that’s weakened, a process called “oil-canning ductwork.”

There’s also a chance that sound is actually a small explosion, something called “ignition roll-out.” To see if this is the source of the sound, pay close attention to your furnace and have someone start it up, either looking inside the furnace doors or listening as the unit starts up. Any shaking or extra burst of flames should be inspected by a licensed HVAC technician as soon as possible.

The Sound of Metal on Metal

Does your furnace sound more like metal scraping together or nails on a chalkboard? If so, the problem is likely with the blower wheel inside your furnace. You’ll want to shut off your unit immediately if you hear this sound and contact a heater repair specialist to look at your furnace.

There are a few things that might have happened to trigger the scraping sound:

  • The motor mount failed, which caused the entire blower assembly or wheel to scrape against the furnace housing.
  • The blower wheel loosened from the motor shaft and is knocking against the blower casing.
  • The blower wheel simply needs replacement.

Banging or Popping When the Furnace Switches On

A furnace that sounds more like a garage band warming up likely has one of two issues, possibly both. Your metal ducts might be expanding and contracting, which is often due to them being too small or of poor quality. You might also need to clean your furnace burners. Dirt on furnace burners keeps them from igniting as they should, which causes a block in the flow of gas. When the gas is finally able to burn as it should, it does so with a bang. In both cases, you’ll want to get in touch with one of our technicians to take a look at your unit and find a solution.

High-Pitched Squealing

A malfunctioning inducer draft motor or blower wheel is often the reason for any squealing or whining you hear from your furnace. There’s also a chance your unit’s shaft bearings need to be oiled up to smooth out their performance. You may need to simply replace or fix your blower or inducer motor.

One thing to note with a squealing furnace is that it’s not one of the more serious furnace issues, meaning you don’t have to arrange for emergency repair services. That being said, you do want to have the issue taken care of sooner rather than later to prevent other expensive problems.

Clicking or Rattling Noises

Hearing a rattling or tapping noise coming from your furnace? A common cause is paper or debris caught in the blower wheel. Removing it can often solve the tapping noise. Make sure the unit is powered off before removing anything caught in the blower.

If removing any debris doesn’t stop the noise, something could be coming loose inside your furnace. Unlike high-pitched squealing noises, rattling is an issue that needs to be attended to ASAP. You might need a repair or replacement before your furnace can operate normally again.

If it’s a clicking noise you hear from your furnace, the culprit is likely the ignition system. The noise is the result of the spark igniter attempting and failing to trigger the pilot light, which also prevents proper furnace function. To find the cause of the clicking noise, light the pilot to see if it sparks.

Reasons to Keep Your Furnace in Good Shape

We understand that you might not want to spend extra money on upkeep, but doing so actually saves you money in the long run. Additional reasons to properly maintain your furnace with regular tune-ups include:

  • Extending the overall life of your unit, which means not having to buy a new one sooner than necessary.
  • Making your home safer, healthier and more comfortable.
  • Lowering the chances of unexpected breakdowns.
  • Keeping your energy costs as low as possible.

Mission AC & Plumbing is more than happy to work with you to figure out a solid maintenance schedule for your HVAC system. The age of your unit, how often you use it and its general condition are just some of the factors that determine how often it should be serviced by a professional.

The next time you hear an odd noise coming from your furnace, be sure to contact Mission AC. We’re here to keep your unit quietly performing at its best all year round.


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