Most mechanical devices make some noise when they operate. Furnaces aren’t an exception, but a properly functioning furnace shouldn’t make too much noise. If your furnace starts making loud and unusual sounds, there’s probably something wrong with it, and it may require repairs. That said, here are some common furnace sounds and the most likely reasons for them.

1. Scraping Noises

Scraping noises may indicate there’s an issue with your blower wheel. A scraping noise can be pretty alarming because it sounds like metal rubbing against metal.

Your blower wheel may make a scraping sound for various reasons. First, it may be broken, and it may need replacement. It may have also become loose, resulting in a scraping noise due to it pounding against the blower casing.

Turn your furnace off immediately, and call a technician to inspect it if it starts making a scraping noise. A scraping sound could point to a serious issue with your blower wheel, and it can lead to considerable wear and tear on your system if left unresolved.

2. Squealing and Screeching Noises

Squealing and screeching sounds are usually due to an issue with the blower motor. The motor has bearings that are prone to drying over time. Motor bearing issues can usually be resolved by adding lubricant. Ensure you use a suitable lubricant (either a mineral or synthetic oil) if you choose to apply the lubrication yourself.

A broken belt may also cause squealing and screeching sounds. Contact a professional furnace technician to assist you with belt replacement to prevent your furnace from malfunctioning.

3. Whistling Noises

Like squealing or screeching noises, whistling is caused by issues with the blower motor. The blower may sometimes develop low airflow issues. Low airflow may cause the blower to strain to draw in enough air to be heated, resulting in whistling. If your furnace starts making a high-pitched whistling sound, consider changing your air filter or opening all vents to resolve the issue. If these fixes prove ineffective, contact a furnace technician for further assistance.

4. Banging and Popping Noises

Banging and popping sounds are normal. Often, furnaces make these sounds as the ducts expand and contract. However, if the banging and popping sounds are exceptionally loud and frequent, it could signal a problem with your furnace. Ductwork issues often cause loud bangs and pops. These sounds are also caused by dirty burners that delay ignition. If your furnace starts making loud banging and popping noises, don’t ignore the problem. It could crack the heat exchanger, which could compromise your safety and lead to costly repairs.

5. Rattling Sounds

A rattling sound coming from the furnace most likely means there’s a loose panel or door. Look to see if the panels and doors outside your furnace are firmly fixed, and tighten any loose screws to resolve the problem.

If that doesn’t solve the problem, it could indicate a loose part. Furnaces are intricate mechanical devices with constantly moving parts. These parts can become loose over time, especially if they weren’t tightened properly. Turn off your furnace, and contact a professional to help you tighten the loose parts.

Often, loose panels, doors, and parts are the main cause of rattling. However, in severe cases, rattling could mean there’s a crack in your heat exchanger. A malfunctioning heat exchanger can leak carbon monoxide into your home, making it dangerous. Contact a furnace technician immediately if the rattling sound doesn’t prevent carbon monoxide poisoning.

6. Rumbling Sounds

If your furnace completes a cycle, you may hear a slight woosh or roaring sound. But if it produces a loud rumble, it could spell trouble. A loud rumbling sound produced after a cycle may indicate an issue with the burner. A rumbling sound is often caused when fuel continues to burn in the combustion chamber even though the burners are turned off.

A rumbling sound shouldn’t be left unresolved. If your furnace starts making a rumbling sound, call a furnace contractor immediately to prevent the risk of carbon monoxide poisoning.

7. Humming or Buzzing Sounds

A low humming noise coming from your furnace isn’t a cause for alarm. Many furnaces produce a dull humming sound while running. However, if your furnace produces a loud humming or buzzing sound, there could be an issue with the motor. It could also indicate there’s something wrong with the fan. Contact a furnace contractor to inspect the electrical components if it makes loud humming or buzzing sounds throughout its operation.

8. Thwapping Sound

Thwapping isn’t as alarming or distracting as many of the sounds already mentioned. It sounds like a card in the spokes of a bicycle tire, and it’s usually caused when something interferes with the blower blades or touches the blower from inside the unit.

Generally, thwapping isn’t a major cause for concern, but it can cause the belt or motor to wear out more quickly than expected if the problem is not resolved. Wear and tear to the motor can cause it to work harder than it should and reduce furnace efficiency. If your furnace makes a constant thwapping sound, call in a professional to inspect it to restore its efficiency and prevent costly repairs down the road.

9. Clicking Sounds

When you fire your furnace up, it may make a clicking sound. The clicking sound it makes when it starts running is normal. However, if the clicking persists throughout the heating cycle, there’s a problem with your furnace.

Repeated clicking often means there’s a problem with the ignition system. If your furnace can’t ignite, it may produce a clicking sound as the igniter struggles to come on.

Ignition system problems are usually caused by issues like:

  • Dirty burners
  • A defective ignition board or valve
  • Damaged flame sensors

Besides the ignition system issues above, compressor or control panel issues may also result in clicking sounds. Additionally, a faulty fan motor can cause clicking sounds. Contact a professional technician to inspect your furnace if it makes repeated clicking sounds.

Ultimately, knowing the difference between normal and abnormal furnace sounds is the first step towards determining whether you have an issue that’s harmless or one that’s a major cause for concern. Low humming sounds and clicking sounds at the start of the cycle usually aren’t a cause for alarm. But if your furnace starts making loud banging, rattling, whistling, and screeching sounds, then you’ll want to get to the root of the problem.

As a rule of thumb, you should call in a furnace technician to inspect your furnace if it starts making unusual sounds that you’ve never heard before. Our technicians will conduct a thorough inspection, identify the problem, and recommend the best course of action to resolve the issue. Often, repairs are sufficient to stop furnace noise, but our technicians may sometimes recommend furnace replacement.

Contact Triple A Air Conditioning & Heating if your furnace starts making unusual sounds. We serve residents of Flower Mound, TX, and the surrounding areas. As a BBB-accredited company, we can provide you with a professional and honest assessment of why your furnace is making strange noises. We also offer annual maintenance that can help you prevent unusual furnace sounds and help with any heating or cooling issues. Call us today if you need us to restore comfort in your home.

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