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Common Furnace Noises And Their Meanings, Explained

There will likely be a bit of noise when your furnace is in operation. However, some noises are an indicator of a serious problem. Furnace noises can occur due to a cracked heat exchanger, a loose belt, dirty burners, undersized air ducts, and compressor problems. 

Some are normal operating noises and should not worry you. But how do you differentiate the noises? 

In this article, we explain the normal operating furnace noises. We also discuss in great detail all the other possible types of noise that a furnace can make and give solutions. 

Normal Operating Noises

An electric furnace heater (Image from Unsplash).

The following noises should not cause alarm. 

  • Pop or click sound: Occurs when the furnace starts a cycle. Warm air hits the cold metal duct, causing the popping/clicking sound as the metal expands. 
  • Clicking sound: This is common when the heat cycle of a gas furnace starts and stops. 
  • Soft or low humming: The sound stems from the furnace blower motor or a draft inducer motor. When the thermostat requests heat, the draft inducer hums or cycles. As the blower motor cycles the air around the home, it produces a low humming sound.  

Continuous Rumbling or Booming Noises

Hearing a loud rumble after the furnace completes a cycle means the fuel still burns, even after shutting down the burners. The problem is either the pilot light, flame sensors, or burners. 

A delayed gas ignition noise occurs as soon as you start the furnace. You’ll hear a booming noise if this is the case. Delayed gas ignition occurs when there is too much gas or air or delay due to a worn-out, dirty, or faulty component. 

You’ll hear a rumbling noise if the pilot light is having difficulty staying lit. 

Don’t be surprised when you hear your furnace making a gurgling noise, especially if it’s a newer, highly efficient model. The gurgling noise occurs due to a faulty condensate pump or excessive condensation in the furnace 

Solutions

You should contact a technician who cleans the unit and tests the pilot light before making the necessary repairs. 

Get a technician to replace the condensate pump. 

Loud Bangs or Banging Noises

Fire/Smoke detector (Image from Pixabay). 

When the metal of the furnace air ducts expands or contracts, the ducts produce banging noises. Undersized air ducts are the main reason for the noise. Extreme air pressure causes the metal ducts to contract and expand, causing occasional loud bangs as the metal pops. 

Loud bangs indicate a combustion problem in the burner for gas furnaces. In most cases, the burner is dirty, therefore delaying ignition. The gas builds up due to the delay and explodes, causing loud bangs when ignition finally occurs. 

If the loud banging of the furnace continues without your intervention, carbon monoxide leaks might occur. Ensure you have carbon monoxide detectors in your home. Avoid carbon monoxide poisoning.

Solutions

Loud bangs require immediate repair as gas accumulation can cause a crack in the heat exchanger. Repairing a heat exchange can be costly, and we recommend buying a new furnace.

Call a technician or the fire brigade once you smell any gas leaks, and stay outside until they come.

High-pitched Whistling or Screeching Noises

Whistling sounds in furnaces, in most instances, result from restricted airflow. A damaged duct is the source of the whistling sound. When the filter has too much dirt, you’ll hear a whistling sound as the air attempts to flow through the dirt. 

Other causes of a furnace’s high-pitched whistling or screeching noise are as follows. 

  • Closed vents: Trying to manage the temperature output by closing vents might also result in screeching or whistling sounds. The vents might not have closed tightly, allowing some air to pass, producing a whistling sound. 
  • Loose components: Loose bolts and fittings can produce a whistling sound. 
  • Gas valve: A damaged gas valve can also produce whistling sounds. 
  • Damaged blower motor: A motor with a mechanical problem can also be the source of the whistling sound. Due to the motor’s vibration, you will hear a high-pitched whistling sound. 

Solutions

You should start by cleaning the debris in all the openings. Wipe down the burners and vents, and change the dirty air filters. For thorough cleaning, engage a duct cleaning professional company. 

Alternatively, you can learn to  How to Clean Your Air Ducts Yourself- Air Duct Cleaning + Maintenance for Beginners!

Remove any furniture or items that obstruct the airflow system of the furnace. 

Call a technician to help repair or replace the damaged gas valve and blower motor while tightening the loose bolts and fittings. 

Clicking or Tapping Noises

A repeated clicking sound without igniting throughout the heating cycle indicates that the control panel or the compressor has a problem. Alternatively, other components, such as the gas valve and thermocouple, are damaged, or the burners are clogged and dirty. 

A continuous clicking sound can also mean a problem with the furnace’s ignition system. As your igniter struggles to come on, it produces a clicking sound. A damaged flame sensor, a dirty burner, or a defective ignition board or valve are the common ignition system problems. 

You must check the flame sensor to see if your furnace is clicking on and off. 

A faulty fan motor can also produce clicking noises. A continuous clicking noise can also be an indication of a defective thermostat. 

Solutions

You’ll have to contact a professional technician to inspect what is making the clicking noises and give recommendations. 

You can also follow our recommendations for a Bryant furnace, not igniting or lighting.

Grinding or Scraping Noises

Bad bearings are the most likely cause of grinding and scraping noises. That usually means you’ve not lubricated the bearings within the furnace blower motor. 

If you hear a scrapping noise, such as a metal sound or a fingernail on a chalkboard, there’s a problem with the blower motor wheel. It is probably broken or has become loose. Immediately turn off your furnace when you hear scraping or grinding noises.  

Solutions

Whenever you hear a grinding noise from your furnace, the first step is to switch it off and call a technician to inspect it. Due to the placement of bearings, a technician is the best person to do the repairs. 

Squealing or Squeaking Noises

A loose or slipped belt is the most common culprit when you hear a squealing sound from your furnace. The squealing noise can also come from a damaged or worn-out belt. 

You’ll also hear a squealing or squeaking sound if the blower motor has a problem 

Solutions

In most instances, adjusting the belt tension will take care of the squealing noise. 

However, you’ll have to call a technician if the squealing noise is from the blower motor. 

Hissing or Whistling Noises

There’s certainly an air leak when you hear a hissing sound from your furnace. So many components in your furnace system can produce a hissing sound due to air leaks. 

The following components are the most common. 

  • Air leaking via ducts that are loose or cracked. 
  • A loose air register cover. 
  • A hissing sound comes from the furnace as air seeps through the duct joints due to an overpowered fan forcing too much wind. 

While most people might ignore the whistling and hissing sounds, they require immediate furnace repair. The heightened force behind the high pressure will weaken the furnace seams. The thin duct walls will start to deteriorate. 

The walls will get holes and cracks, allowing heat loss. Eventually, the heat exchanger, compressor, and blower fan will experience pressure, leading to the unit’s breakdown and costly repairs. 

Due to the inconsistent and inadequate heating, you will likely experience an increase in your energy bills. 

Solutions

Tighten the air register screws. Slow the fan circulation, thereby lowering the unusually high air pressure. 

Clean the debris in all the openings. Change the dirty air filters. Call a technician to determine which component makes the hissing sound and repair or replace it. 

Strange Vibration or Rattling Noises

It’s not normal for a new furnace to have strange vibrations or to produce rattling noises. However, any loose part or a cracked heat exchanger produces rattling noises. 

Rattling noises will also occur if there is a loose door or panel. 

There are several reasons as to why your furnace is vibrating. We highlight them below. 

  • Dirty air filters, 
  • Blower wheel issue, 
  • Ignition problems, 
  • Contraction and expansion of ductworks,
  • Loose parts. 

When the bearings of a blower motor wear out, you’ll hear your furnace producing a humming sound. Worn-out bearings will cause the furnace to become unbalanced and vibrate. 

Solutions

Fix any loose part or replace it. Tighten the door or panel if you can easily see the problem. If the rattling sound does not stop, an internal part is loose. If that is the case, you must call an HVAC professional.

Replacing the cracked heat exchanger might be costly, and buying a new furnace is the best action here. 

Author

  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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