Some furnace noises are just normal mechanical sounds while other noises can mean mechanical malfunction. There are many online discussions about furnace noises because so many people experience the same thing in their Hallsville or Gladwater homes. The fact is, there are a variety of sources for furnace noise — some serious, some signaling the need for future attention, and some that are noises you may choose to live with. Learn how to distinguish what those furnace noises are and how seriously you need to take them.

What's That Noise?

Furnace noise comes in a variety of pops, bangs, whistles and whines, rattles and hums. While you should always get a professional to diagnose a noise properly, here's a brief list of sounds your furnace may be making:

  • Low rumble
  • Squeal
  • Motor hum
  • Rattling
  • Boom or popping when heat comes on
  • Whistling from vents
  • Clicking

What to Do?

Troubleshooting these various noises and their causes is obviously for the expert, but it never hurts to have a better understanding of how your system works, and awareness as to what might go wrong.

Most of us grow familiar with the sounds the heating system makes during normal operation, so it can be disturbing when we notice something new. Sometimes, if you address the noise quickly, you can prevent further deterioration and a costly repair. 

Let's analyze some of the noises listed above, and the implications for the system once the problem arises.

  • Low rumble: When you hear a rumble from the furnace, it could be that the air filter isn't doing its job of keeping contamination out of the system. Check the filter and change it if it's dirty.
     
  • High-pitched squeal: This sound can result from ball bearings that need lubrication.
     
  • Low hum: A humming sound can be a signal that a motor is failing. If a motor has been overworked and hasn't had the proper maintenance, it may start to die. 
     
  • Rattling: If the rattling is due to carbon monoxide leaks from a cracked heat exchanger, this requires urgent attention. 
     
  • Popping or booms: Sometimes these booms or pops are caused by the ductwork expanding as the system comes on. Often, after a duct cleaning, homeowners report that these sounds weren't occurring before. That's because prior to cleaning, the pressure in the ducts was diminished by dirt and debris on the duct walls, the fan, the coils and in the return vents. After cleaning, the pressure is more intense and the popping or boom ensues. 

    Systems that haven't been cleaned may also produce booms or pops when the heating comes on and as the duct walls expand.

    Popping and booming may also be caused by delayed ignition due to dirt buildup on the burners. Test for this condition by having someone stand by the furnace while you call for heat at the thermostat. If you hear a boom within the furnace many seconds or even minutes after the adjustment to the thermostat, or if flame from the burners doesn't appear for a good while, chances are you have a clogged burner. Make sure you get it cleaned, or you could risk a cracked heat exchanger. 
     

  • Whistling vents: Whistling vents are probably not a major issue, and if whistling is caused by an improperly sized vent cover, it may be an issue you just have to learn to live with. If the whistling proves too annoying, you might lower the fan speed — but only in winter. You shouldn't do this when the air conditioner is on or you could risk freezing the coils.
     
  • Clicking: This can be due to a variety of causes, including a loose fan in an older oil-powered furnace, worn bearings in the fan, a faulty gas valve (intermittent clicking), faulty pilot light with gas furnaces, gas issues or faulty wiring.

    If you have an older oil-powered furnace and you hear clicking, chances are its due to a worn fan. Soot buildup can also impede the performance of the fan. Worn bearings should be replaced immediately before the motor burns out, while a faulty gas valve should be fixed by the homeowner's gas provider.

    Pilot lights can wear out over time, and may need to be replaced. Don't hesitate to call a professional when you have pilot light issues. 

JD's A/C is here to help you diagnose the reasons for any mysterious furnace noise and other HVAC issues you may have. We serve Longview and the surrounding area. 

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