Why is My Furnace Making a Loud Noise? A Phoenix Tech Answers

It’s normal to hear some dull humming noise while your furnace runs, or a little pop when the system first turns on. However, if you’re hearing consistent, loud sounds it could mean there’s a problem a professional will need to fix.

In this blog, we’ll explain what causes 4 common furnace noises:

Scroll to the section that best describes the noise you’re hearing.

Hear a banging or popping sound coming from the furnace?

These sounds are most likely the result of:

• Delayed gas ignition
• Expanding/contracting ducts

If you hear a banging sound when the furnace first starts, it could be caused by a delayed ignition. When a furnace doesn’t ignite right away, gas builds up in the combustion chamber. Once the furnace ignites, the excess gas combusts and makes a loud banging sound.

The delayed ignition problem could be caused by:

• Restricted gas supply
• Misaligned burners
• Faulty electronic ignition system

Solution: A professional will need to inspect the furnace and fix whatever is causing the delayed ignition issue.

Do you hear a metal popping or banging sound when your furnace is running? If so, this could be the sound of the ducts expanding or contracting due to pressure changes.

Some popping is normal, but if it is persistent and loud, you may have one of the following issues:

• A clogged air filter
• Too many closed air vents
• Undersized ducts

Solution: First, make sure your air filter is clean (if it’s dirty, replace it with a new one). Then, make sure air vents are open (even in unused rooms). Let your furnace run for a while and see if the popping sound stops or becomes less distracting.

If the popping noise persists, you may have a bigger issue, such as incorrectly sized ductwork. An HVAC professional will need to inspect your ductwork and measure the pressure inside the ducts. After the inspection, the professional may recommend replacing or modifying your ductwork to eliminate or reduce the popping noise.

A squeaking or squealing noise is most likely caused by a problem with the furnace blower. (The blower is the part of your furnace that brings in cool air to be heated, then pushes warm air back into your home.)

Common blower problems that create a squeaking noise include:

• A worn motor belt
• Worn blower motor bearings

Solution: Each of these issues will need to be addressed by an HVAC professional. For more information about these blower problems, refer to our blog, “Why Is My Furnace Blower Fan Squeaking?.”

Hear a buzzing or humming noise coming from your furnace? If so, that most likely is a sign of an electrical problem.

Common furnace electrical issues include:

• A worn or failing motor
• Failing transformer
• Failed blower motor capacitor

Solution: Because these problems require extensive electrical knowledge to diagnose and repair, you’ll need to contact a certified HVAC professional for assistance.

If you hear a rattling or clanging sound coming from your furnace, the most likely reason is that a part is loose in the system.

Did you recently service your furnace or have a part repaired? If so, maybe a screw needs to be tightened in the access panel or an internal component needs to be refastened.

Although it’s less common, a rattling sound could signify that there’s a crack in the heat exchanger. The heat exchanger is a series of metal coils that are responsible for heating your home’s air. If your furnace has overheated, the coils can crack and produce a rattling sound after the furnace first turns on. If the heat exchanger has cracks, you’ll need to have it replaced.

Solution: Contact an HVAC technician to find the source of the rattling and repair the problem.