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Strange Furnace Sounds

strange furnace sounds

Furnace Noises You Should Never Ignore

We would all like for the appliances in our homes to operate smoothly and soundlessly. However, we know furnaces are known for their strange noises. If you have noticed lately that your furnace is noisier than usual, or you start hearing a new sound this most likely is a sign that something may be wrong with your furnace. Below we discuss what are considered normal or strange furnace sounds and when it may be time to contact a professional about maintenance or repairs. Having the ability to determine strange sounds will help you feel more at ease as a homeowner, and help you act quickly when needed. This can potentially help you avoid a costly repair or even untimely replacement.

Normal Furnace Sounds

When a furnace first starts up the heating cycle, most homeowners will notice some slight noises. This startup sound is not something to worry about. You may hear a little pop or click as the furnace starts and then a slight hum as it continues to run. These start up sounds should not be so disruptive to your household members. Also keep in mind, that older furnaces will be a bit louder than a newer furnace. This is a result of newer models being designed with additional features to limit the sounds you hear. Furthermore, a variable speed system will make even less noticeable sounds as it makes minor adjustments.


A loud banging sound when the furnace first turns on could be an issue with the ignition. A weak flame or dirty or clogged burners maydelay the ignition. A delayed start can lead to a small amount of gas in the combustion chamber, so when ignition does start the built-up gas will “explode” with the sound traveling throughout your home by way of the ducts. Dirty burners can be avoided by scheduling routine maintenance. Any problems with the furnace ignition the system should be looked at by a trained technician right away. Another reason you may hear banging, booming, or popping is a result of your metal ducts expanding and contracting with changes in the temperature. It is not usually cause for concern and it is a fairly common problem. To minimize the sounds there are solutions such as insulating ducts, replacing undersized ducts, adjusting dampers, or replacing the air filter.


If you hear loud rumbling that continues after your furnace has completed a cycle and switched off, this is a cause for concern. It could be a sign that fuel is continuing to burn in the combustion chamber even though the burners are off. It usually indicates problems with the burners, pilot light, flame sensors and a furnace that has not been maintained in a while. Professional intervention is necessary because this type of situation increases the risk of carbon monoxide poisoning from the extra fuel in the combustion chamber. Turn your furnace off and schedule a furnace repair service right away.

Whistling or Wheezing

Whistling or wheezing sounds indicate an issue with the airflow. Most likely it is due to a dirty air filter that needs to be cleaned or replaced. When your filter is full of particles and contaminants, your furnace is still trying to push air through, causing the whistling or wheezing sound. Other causes could be a blocked return, closed vents or dampers. Contact a professional if the sound continues after replacing filter and opening vents. In some cases, it is best for a trained technician to address the issue as it can indicate an issue with the blower or burner, or improperly sized furnace.

Clunking or Thumping

Clunking or thumping furnace sounds could indicate an unbalanced motor or blower wheel. Another reason for these sounds could a fan belt that has cracked or split and is hitting other parts as it rotates. The best step you can take in this situation is to turn your furnace off and call for furnace repair. The blower wheel and motor are essential furnace components you do not want bouncing around.


For the most part a low hum is a normal sound when the furnace runs and is not cause for alarm.  However, there are times when the humming sound can be a cause for concern. If the noise is loud during a cycle or comes on when it was not present before it could be an issue with the fan or capacitor. If the sound persists throughout operation, then it could signal an issue with the motor. Pay attention to the volume and when the sound is present and contact a technician to inspect the system.

Screeching or Scraping

Screeching or scraping may indicate metal against metal. It may signal a loose blower fan and blades scraping the casing of the furnace or other parts in the furnace have loosened. Scraping can also indicate dry bearings, which need routine lubrication to function properly.


A rattling furnace sound can indicate a loose panel or loose screws. However, it could also be a sign of a leak or crack in the heat exchanger which can leak dangerous and potentially lethal carbon monoxide in your home.


Clicking sounds at furnace startup and shut off is normal. However, if the clicking happens continuously throughout the heating cycle it could indicate an issue with the compressor or control panel.

Easy Solutions for Furnace Noises

It is important not to ignore the signs of a failing HVAC system and not to get accustomed to any unusual loud furnace sounds. Any strange, unusual noises mean your system is trying to signal an issue with your equipment. By neglecting the sound or postponing repair it could cause potentially costly damage to the system or hurt your home and family.  To help your furnace operate more quietly and efficiently, change your air filter often and schedule routine HVAC maintenance.  A technician will adjust and clean furnace components during routine furnace maintenance helping to minimize strange furnace sounds.

Contact LA Construction, Heating and Air

If you notice any unusual furnace sounds or if your furnace is not working properly, do not wait to call us to schedule an appointment. One of our trained technicians will inspect your furnace and recommend routine maintenance, repair or replacement. Give us a call today at 818-341-3406 or contact us online.

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