Furnace Noises Explained: Causes, Fixes & When to Worry

So you hear a loud screeching noise from your basement and you immediately think, “oh great, that doesn’t sound good and what is this going to cost me?”. Unless you’re keeping a bat horde in your basement, the noise is probably from your furnace.

If you’re wondering about furnace noises and what they mean, you’ve come to the right place!

Furnace noises indicate that something is wrong with your furnace, and it’s due for repairs. You can choose to ignore these noises, but doing so will work to your detriment. Your best bet is to find the source of the noise and solve the problem once and for all.

This post highlights some of the common causes of a noisy furnace. We also show you how to take care of these noises and keep your furnace in good shape.

Furnace Noises Explained

Modern furnaces tend to be very quiet, but they do still make noises like clicking, low humming, and pinging or rattling as the system cools down after a heating cycle.

But if your furnace is making a loud noise or weird sounds, it’s typically an indication that something is wrong. This is especially true if you hear a new noise or if an existing noise changes or gets worse.

While you can’t necessarily diagnose a problem based solely on furnace noises, they can give you an idea of what might be wrong, so it’s good to know what the difference sounds can mean.

What are Normal Furnace Noises?

No furnace is completely silent, and normal furnace noises can include:

• Clicking: Clicks when the furnace starts or stops is normal
• Whooshing or rushing air: Usually the sound of air moving through the ducts and vents
• Humming: The sound of the blower motor running
• Popping or ticking: From metal ductwork expanding and contracting as it heats up and cools down
• Gentle roaring: The sound of burners igniting and running steadily
• Chirping: Normal at the beginning of heating season, but should go away after the system gets up and running

However, there are times when these noises can also indicate a problem. As such, it’s always best to have your furnace serviced annually by a professional HVAC expert. And make sure to mention if your furnace has been making new sounds!

What are Irregular Furnace Noises?

You know there’s most likely a problem with your heating system when your furnace is making sounds like:

• Banging
• Scraping
• Grinding
• Whistling
• Popping
• Rumbling
• Thumping
• Humming
• Shrieking
• Squealing
• Clicking
• Rattling
• Hissing

The different types of sounds can indicate problems with various components, including the blower, ductwork, filter, ball bearings, ignition system, and beyond.

Let’s look at these furnace noises and what they can indicate.

Furnace Is Making Scraping or Grinding Sounds

This issue is often caused by loose or broken parts, and the sound you’re hearing is typically two objects, often metal, rubbing against each other.

Possible Causes: Loose Blower Wheel or Worn-Out Ball Bearings

Scraping sounds from your furnace indicate that its ball bearings may have worn out. You could also have a loose blower wheel in your HVAC. 

Don’t make the mistake of trying to fix this on your own. These are super sensitive parts of the furnace, and you could worsen the situation. The best thing to do is to turn it off and contact a professional HVAC service ASAP.

Furnace Is Making Rumbling or Thumping Sounds

Rumbling and thumping furnace noises are a sure sign that you should call an HVAC pro. Not only is it potentially dangerous, but it could cause major damage to the system.

Possible Causes: Loose/Unbalanced Component or Burner Problem

Rumbling noises can happen because of dirty burners and delayed ignition, which cause gas to build up and result in a small explosion when the furnace fires up.

Incessant rumbling sounds can also signify that you have one or two loose or unbalanced parts, such as the motor or blower wheel.

If you don’t address the issue immediately, these loose parts may come off completely. Once they do, they can interfere with the normal functioning of other parts of your furnace.

You’ll need to contact HVAC pros so they can get to the root of the problem. They’ll inspect the heat exchanger, blower motor, and gas burner. From there, they can tell you whether they can secure the loose parts or whether you need to replace them.

Furnace Is Making Banging Sounds

A loud booming or banging sound from your furnace can be extremely alarming, and it can indicate similar problems as rumbling and thumping sounds. In other words, get it checked out right away!

Possible Causes: Delayed Ignition or Expanding and Contracting Ductwork

Banging is one of the common furnace noises that can indicate a problem. It can mean there’s a delay in your ignition that causes a mini-explosion, producing that loud bang. 

Gas continues to build up in the combustion chamber while the ignition delays. When the ignition finally comes on, all the gas will light up at once, leading to the bang. Delays in the ignition are primarily because of a clog or problems with the gas chamber.

We highly advise against fixing the ignition and combustion chamber by yourself. One wrong move could result in huge gas leakage, a recipe for disaster. To be on the safe side, call a professional HVAC service to help you handle the situation.

Furnace Is Making Whistling or Hissing Sounds

Chirping is a normal sound if you haven’t used your heating system in a while, but if your furnace is making a whistling or hissing sound, it could mean a different problem.

Possible Causes: Clogged Air Filters or Duct Leaks

An incessant whistling or hissing sound often means the furnace filter is dirty and restricting airflow. It can also mean an air leak in the ductwork.

More seriously, hissing and whistling can indicate a gas leak. If you smell gas, get out of the house immediately and call your gas company.

To solve this problem, inspect the ducts for leaks and change the furnace filter. Ensure you change your filter every three months for the most significant effect. Remember, a filter that stays too long compromises your home’s air quality.

That said, you might want to check out our air filter buying guide if you’re looking to have pristine air quality in your home.

Furnace Is Making Humming or Buzzing Sounds

Humming and buzzing aren’t furnace noises you should ignore. If your furnace is making a buzzing noise or a furnace humming sound, it’s probably because some problem is causing components to vibrate.

Possible Causes: Issues with the Blower Motor or Loose Parts

Humming noises are a sign that something could be wrong with your blower motor or capacitor.

Furnace blower motor noise is nothing to smile about and deserves your attention ASAP.

Another potential cause is a loose or imbalanced part, such as a mounting bolt or bracket, fan blades, bearings, or blower wheel.

Contact your local HVAC repairman to help alleviate the issue before things get out of hand.

Furnace Is Making Shrieking Noises

Hands down one of the scariest furnace noises is shrieking! This high-pitched sound almost feels like the furnace is screaming for your attention, and it is.

Possible Causes: Worn-Out Blower Belt or Motor Bearings

This is another problem with the blower motor, and it likely has a worn or damaged belt.

If you hear even the slightest hint of a shrieking noise from your furnace, contact HVAC professionals ASAP. If you can catch the problem early enough, you may be able to solve it before it worsens. Shrug it off, and you may have to get another belt for your blower motor.

Furnace Is Making Popping Noises

Many furnaces make popping noises when you first fire it up at the beginning of heating season. But a furnace knocking sound or popping sound that’s new or that continues after the furnace has warmed up is something you have to pay attention to.

Possible Causes: Ductwork Expansion and Contraction

The popping noises from your furnace almost sound benign, but they’re not. If your furnace is making a noise like this, it is most likely because your air ducts are expanding. 

The blower motor will disperse warm air into the air ducts when the air cycle starts. The metal forming the air ducts expands to accommodate the warm air from the blower fan, causing a popping sound.

Alternatively, the sound may be a result of contamination in the burner. The older your furnace gets, the more sediment collects on your burner. That’s why you must arrange to remove this debris from your burner every year.

Failure to do so can result in improper combustion and may lead to damaging your heat exchanger, which would probably mean replacing the furnace.

Furnace Is Making Squealing Noises

Squealing and screeching sounds from a furnace don’t just indicate a problem—they can also be extremely disruptive!

Possible Causes: Worn-Out Blower Belt and Other Blower Problems

In an older furnace, one potential cause is a worn, loose, or misaligned blower belt (newer furnaces don’t typically have these).

Other possible causes of these furnace noises include dry or worn blower motor bearings, a loose or misaligned blower wheel, and a failing blower motor.

However, a clogged air filter can also cause squealing and screeching.

Furnace Is Making Clicking Sounds

Like with popping, a clicking sound from a furnace can just be the noise from it first firing up. If that’s the only time you hear it, the furnace is probably fine.

Possible Causes: Issues with the Ignition System

You have to worry about a furnace clicking sound when the noise is persistent, excessive, gets louder, or changes.

It can potentially indicate a cracked heat exchanger, but the more likely cause is a problem with the ignition system, such as a dirty flame sensor, pilot light/igniter failure, or loose wiring.

Furnace is Making Rattling Sounds

Like with scraping, rumbling, and some other furnace noises, rattling can often indicate a loose part.

Possible Causes: Loose Parts or Dirt/Debris

Rattling sounds from a furnace can be a sign of loose ductwork, panel, screws, blower wheel, or even heat exchanger.

Other potential causes include a dirty air filter or debris inside the furnace (like leaves, screws, or dirt) that’s rattling around.

Diagnosing Furnace Noises

When your furnace is making noise, you can often use the specific sound to help diagnose the problem.

While it’s generally a good idea to have a professional HVAC contractor diagnose strange furnace noises, this step-by-step guide will help you identify possible problems:

• Step 1:Identify the type of noise, such as banging, clicking, whistling, etc.
• Step 2: Figure out where the noise is coming from, such as the ducts, burner, vents, blower, etc.
• Step 3: Identify possible causes based on today’s discussion
• Step 4:Perform basic troubleshooting, which can include cleaning filters, clearing the space in front of vents, looking for leaks in the ductwork, checking for loose parts, tightening screws, etc.

DIY Troubleshooting Tips and When to Contact a Professional HVAC Technician

There are plenty of instances when you shouldn’t attempt furnace maintenance, troubleshooting, or repairs and should instead leave the work to the pros. That includes if you don’t have the:

• Necessary knowledge
• Right tools
• Ability to diagnose the problem
• Confidence to address the problem yourself

However, if you are properly prepared with the knowledge, tools, and experience, there are some furnace noises you might be able to address by yourself, including:

• Whistling or hissing if it’s a clogged air filter, blocked vent, or leaky duct
• Rattling or vibrating if it’s a loose panel, screw, or similar component
• Clicking if it’s just the furnace heating up
• Thumping or knocking if something needs to be tightened
• Humming or buzzing if it’s a loose component or debris inside the furnace that you can remove

By contrast, noises like banging, booming, screeching, squealing, and grinding generally always require the expertise of an HVAC professional.

Preventative Maintenance to Avoid Furnace Noises

Furnaces need some regular TLC to work optimally and efficiently. Annual inspections, repairs, and most maintenance should be addressed by a licensed HVAC professional, but here are some preventative maintenance steps you can take to avoid furnace noises that could mean trouble:

• Clean or change the filter every one to three months
• Vacuum the blower motor, blades, and burner
• Clean the heat exchanger with a non-abrasive pad
• Scrub the flame sensor
• Remove obstructions from around the vents
• Clean and dust the vents

Conclusion

The next time you hear furnace noises, this guide will help you figure out if you can diagnose and address the problem or if you need to call a local HVAC pro.

Request a quote today and we’ll help you find the best HVAC contractor for your furnace.

Read More: 22 Common Furnace Problems with Troubleshooting Tips