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Why Is My Furnace Making Loud Noises? A Texas HVAC Technician Explains

November 11, 2019

Tired of that obnoxious noise coming from your furnace?

We’ll help you troubleshoot what could be causing that noise, and how to fix it.

In this article, we’ll cover 5 common furnaces noises:

  1. Rumbling noise
  2. Grinding noise
  3. Rattling noise
  4. Knocking noise
  5. Buzzing noise

Let’s start with noise #1... Want a technician to repair your furnace and stop the noise? We can help!

Noise #1: Rumbling noise

Is your furnace making a loud rumbling noise?

If so, it could be caused by one of the following issues:

  1. Dirty gas burners
  2. Dirty draft inducer motor
  3. Broken pilot light

Let’s look at each of these issues in more detail below:

Dirty gas burners

Dirty gas burners are the most common culprits of a rumbling furnace.

furnace diagram labeled burners

The burners in a gas furnace

Over time, soot and dirt build up on the burners, which restricts the airflow needed for combustion. As a result, you’ll often hear a deep, rumbling sound when your furnace kicks on and while it runs.

Solution: Contact a furnace professional to clean the burners and see if that fixes the noise.

Dirty draft inducer motor

The draft inducer is a small fan inside your furnace located near the part that heats your home’s air (the heat exchanger).

The draft inducer has 2 jobs:

  1. Keeps your furnace running safely: The draft inducer takes the gases produced during combustion and pushes them out of your furnace via the flue pipe. If those combustion gases were to stay inside the heat exchanger, there could be a small explosion when the burners ignited again.
  2. Improves energy efficiency: When the draft inducer sends fresh oxygen to the burners, it allows the burners to run efficiently, which improves your system’s energy efficiency.

If the draft inducer is dirty or loose, it could cause a rumbling sound when your furnace kicks on.

Solution: Have a furnace repair person inspect the draft inducer to make sure it’s secured and clean.

Broken pilot light

If you have an older furnace (20+ years old), you may have a pilot light issue.

When a pilot light is not adjusted correctly, or is covered in soot, it can cause your furnace to emit a rumbling sound.

Solution: Since pilot light technology is very old, it’s probably time to start thinking about a new furnace.

Noise #2: Grinding noise

If you hear a grinding noise, like the sound of metal on metal, usually the issue is with the blower. The blower is the part that’s responsible for pulling air into the furnace to be heated, and pushing warm air back into your home.

The following problems cause the blower to make a grinding noise:

  • The blower wheel is broken or loose, which causes it to hit the side of its housing
  • The motor bearings are worn out

Solution: If possible, turn off your furnace to prevent further wear and tear. Then contact a professional to inspect your blower.

Noise #3: Rattling noise

Often a rattling noise is a sign that something is loose inside your furnace.

Sometimes screws can become loose (or maybe they weren’t tightened correctly) on the metal panels that enclose your furnace. Additionally, parts inside your furnace can become loose from their housing, which could cause the rattling noise.

Solution: You can try tightening the screws using a screwdriver. If the panels still feel loose or that doesn’t fix the rattling noise problem, contact a professional for help. They’ll be able to locate and tighten the loose part.

Note: If you have an old, belt-driven furnace, the rattling noise could be caused by a bad blower motor fan belt. If the belt starts to develop cracks and wear out, sometimes you’ll hear a rattling sound while the furnace is running.

Noise #4: Knocking noise

A loud knocking or banging sound can be caused by two main issues:

  1. Ignition problems
  2. Ductwork contraction and expansion

Ignition problems

In normal operation, your furnace should ignite gas flowing from the burner as soon as the gas valve opens. However, if there is a delay in the ignition, a cloud of unburned gas can accumulate in the combustion chamber. When this cloud does ignite, it can produce a loud banging or knocking sound.

The following problems lead to a delay in the furnace ignition:

  • Broken electronic igniter
  • Dirty or malfunctioning burner
  • Low gas pressure

Solution: A technician will need to inspect your ignition system to see if your furnace has any of the issues listed above.

Ductwork contraction and expansion

During cold weather, metal ducts naturally contract. When the furnace is running, it blows hot air through the ducts, which causes them to expand. This expansion causes the sheet metal to make a knocking or banging sound as it slightly bends outward.

Solution: You’ll need a duct specialist to determine if this is your issue. If you have rectangular ducts, the specialist may recommend replacing them with circular ones. Additionally, they may recommend installing a heavier-gauge metal to reduce the bending caused by expansion.

Noise #5: Buzzing noise

A buzzing or loud humming noise generally means there’s an electrical issue with your furnace.

Common electrical problems that cause a loud buzzing sound include:

  • A failed blower motor capacitor
  • An aging blower motor
  • A broken transformer

Solution: Contract a furnace technician to inspect your system and repair any faulty electrical components.

Ready for a furnace repair? Hire a Texas pro with experience

No matter what furnace noise you’re hearing, our team of trained technicians can quickly diagnose and fix the problem.

Learn more about pricing and what to expect when you hire us to fix your furnace by visiting our furnace repair page.

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