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Furnace Repair in Lakewood - "Why Is My Furnace Making Noises?"

Laura, a homeowner in Lakewood, called us saying that her ancient furnace was making strange noises and wanted us to come take a look at it.

So, what was the cause of the noise? Well, before we get to that, let's say that furnaces can make all sorts of noises. Some of the more common noises include:

  • Metal scraping.
  • Squealing.
  • Loud popping or banging.

So, if your furnace is making any of those noises, read on. We’ll briefly explain their most likely causes and how to fix them. And then we’ll explain how we fixed Laura’s noisy furnace problem.

Metal Scraping Noise

Cause: This sound could be caused by three things:

  1. Blower wheel came loose from the motor shaft, moved, and is hitting the blower housing, causing it to scrape the housing sides.
  2. Blower wheel actually broke and is hitting the housing sides.
  3. Motor mount broke, the entire motor and blower assembly dropped, which caused the blower wheel to hit the housing.

Solution: Hurry and turn off your furnace! You need to minimize damage.

If the cause was #1 and no damage was done to the wheel or the motor shaft, a technician could move the blower wheel back to its proper spot and retighten it. For all other issues, the technician will have to replace the parts needed.


Cause: The belt that connects the motor to the fan is loose or has slipped.

Solution: Call a furnace technician to replace or tighten the belt as needed. Make sure you find a good tech who knows what they’re doing because tensioning a belt past the required torque can actually shorten its life.

Popping/Banging Noise

Cause: If you hear this noise when the furnace’s fan first starts and/or stops, the issue is that the furnace is starved for air.

What do we mean?

Well, when the furnace blower turns on, it sucks air in through your return vents.

A return vent

And when the blower struggles to pull in enough air, metal sheet ductwork will pop or bang inward due to the extra negative pressure. In other words, the pressure inside the ductwork is much lower than the pressure surrounding it, causing the ductwork to pop in when the blower starts and pop back out when the blower stops.

The cause of this air starvation could be:

  • Undersized return ducts.
  • Too few return ducts.
  • Blocked return vents.
  • Dirty air filter.

Solution: First, see if the air filter is dirty. Change it if it looks like the one on the right in this picture:

Clean filter (left) next to a dirty filter (right)

If that’s not the cause, contact a furnace tech to investigate the issue further.

So, What Was Causing Laura’s Furnace Noise?

After a thorough investigation, our technician discovered that Laura’s furnace had two issues:

  • Blower motor was leaking oil and needed to be replaced.
  • Capacitor (basically, a battery that helps the furnace start and keep running) needed to be replaced.

Thankfully, our tech had all the parts in his truck and fixed Laura’s furnace right away.

“Clinton D. arrived within 90 minutes of my original call to the company! He was very courteous, professional, and friendly. Provided excellent information and recommendations. Will definitely use Plumbline again.”

-Laura S. from Lakewood

Need help from a Colorado Plumbing, Heating, Cooling, or Electrical Specialist? 

For your convenience, you can request an appointment in one of two ways:

  • Call us at (303) 436-2525 for immediate assistance.
  • Click on the button below to schedule your appointment online.


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