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Frightening Furnace Noises: Boom, Rattle, Pop!

by vscontent on November 1, 2015

It’s the night after Halloween and you are more attuned than ever to the sounds coming from your home and heating system. Yesterday, while you were making last-minute preparations for trick-or-treaters, you could have sworn you heard a loud boom coming from the basement. Then a whistling sound which turns into a groan.

Furnace Noises

Whatever you are hearing, or think you are hearing, coming from your furnace, we have the answers for you, unless of course it isn’t your furnace! Time to muster up your bravery and find out for sure.

If your ductwork or furnace noises, you might be best off calling in a professional, but if you want to know the causes of common furnaces sounds, keep reading.

Common Furnace Noises and What They Mean

Let’s start with a BANG!


If you hear a loud and sudden bang or boom, it’s probably due to a buildup of gas and a delayed ignition. This is similar to what may happen if you leave the propane gas grill on for too long before igniting it.

There are different reasons for why you may have a delayed ignition, which is why you should call a qualified heating and cooling professional to inspect this as soon as possible.

  • Dirty, clogged burners are causing a delayed ignition. When your furnace finally lights, the gas build-up in the combustion chamber creates a loud BANG or BOOM that reverberates throughout your home.
  • There is an unbalanced air-to-fuel ratio. If there is too much air, or too little gas, this could be causing your gas to build up, leading to the resulting explosion.

Whether it is due to a delayed ignition or a poor air-to-fuel mixture, your furnace will need a professional inspection and cleaning to ensure safe operation. Avoid using your furnace until a professional deems it safe to do so.

Deep Rumbling

A groaning or rumbling furnace noise can indicate a serious problem with your motor bearings, gas burners, or pilot light. A house-shaking rumbling on the other hand could be due to unburnt fuel in your combustion chamber that burns even after your furnace shuts off.

If this is happening, then you could be putting your family at risk of carbon monoxide poisoning. Call your heating professional to get your furnace checked out immediately.


A rattling noise can mean many things. If you are hearing a rattling furnace noise before your blower turns on, this could be due to a cracked heat exchanger.  A cracked heat exchanger is a serious furnace problem that should not be neglected. It is the number one cause of carbon monoxide leaks from your furnace. If you hear a rattling sound before your blower comes on, immediately turn your furnace off and call a professional HVAC technician ASAP! Do not use your furnace again until a professional says it’s safe to do so.

If you hear a rattling sound after your blower comes on, this could be due to loose ductwork connections. This could potentially be solved by DIY sealing your ductwork. If the rattling sound persists, call your local HVAC company to fix the problem. You may need to have professional duct cleaning and sealing. Click here to learn about Pacific Air System’s Aeroseal Duct Sealing technology.

Another cause of persistent rattling and rumbling is an imbalanced blower wheel or motor or a loose screw. This can cause serious issues if neglected. It’s recommended that you call a professional to see if you need a simple repair or a full replacement.

The rattling noise could also be due to a loose panel or other furnace part. This may be simply fixed by tightening your panels, however, the problem may lie deeper within your indoor air handler.


When your furnace kicks on, it is normal to hear a clicking sound. This is just your ignition clicking on. If, however, you hear excessive clicking, you may have a problem with your flame sensor. Over time, your flame sensor gets dust and debris buildup, which prevents proper operation. Call a professional to clean and/or replace your flame sensor.

If your furnace clicks and clicks without ever coming on, this is most likely due to loose wiring or a leaky gas valve. Or if you hear a swooshing/swishing and then a click, this could also mean a leaking gas valve.

A clicking and clacking sound before the blower turns on can indicate a crack in your heat exchanger, a very dangerous proposition.  A leaking gas valve and cracked heat exchanger are serious issues not to be taken lightly. In either case, turn your furnace off immediately to prevent further gas and CO leaks and wait for a qualified HVAC technician to troubleshoot and resolve your problem.

Scraping Metal

Scraping and clanging metallic furnace sounds almost always mean a problem with your blower wheel. Here are the different possible causes of the scraping sound:

  • It’s possible that a screw or something else is stuck in your blower assembly causing the metallic sounds.
  • Your blower wheel has become loose and is scraping against the side of its housing. A professional can tighten your connections to fix this sound.
  • Your blower wheel or motor is broken and needs to be repaired or replaced.

If you hear this metallic scraping from your furnace, turn it off immediately and call your local HVAC professional.


The popping noises you are hearing are probably coming from your ductwork. When air passes through your ductwork, the metal can expand and contract, which causes the popping noises. Although a normal sound without many serious consequences, your HVAC technician will be able to recommend solutions for this problem.


A squealing or whining sound from your furnace usually indicates an air leak, loose blower belt, motor bearings that need oiling, or a malfunctioning blower motor.

Although not as dangerous as the other furnace noises you may be hearing, it is important to address this problem as soon as you can. Neglecting air leaks or blower problems can lead to expensive repairs down the road. Get this fixed as soon as possible to improve energy efficiency, comfort, and the lifespan of your HVAC unit.


A whistling furnace sound could mean a few things, but most likely it is either due to air leaks or a clogged air filter. To solve your whistling problem, change your furnace filter and inspect your duct system for air leaks here.

Watch this video to learn how to change your furnace filter:

Annual Furnace Maintenance

Regular maintenance can prevent all of these noises from happening in the first place. Delaying maintenance or repairs can cause serious safety and efficiency problems. Make sure you schedule heating and cooling maintenance every year; once in the fall for your furnace and once in the spring for your air conditioner.

For more information on your furnace and how to improve energy efficiency and promote comfort and safety in your home, read our other blog articles on the topic:

For more information on gas furnace noises and troubleshooting, contact the HVAC professionals at Pacific Air Systems.

Call Pacific Air Systems Heating & Cooling at (253) 292-3995 for 24/7 service!

Since 1984, we’ve been proudly serving our communities in Federal Way, Graham, Spanaway, University Place, Steilacoom, Sumner, Lakewood, Puyallup, Tacoma and Gig Harbor.

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