Furnace Noises are common ways of telling if there is a problem with your furnace about to happen or happening right now.  Here are a few noises that you shouldn’t ignore.

Loud Scraping Sound

A loud scraping noise that sounds like metal rubbing metal or nails scratching a chalkboard probably means something is wrong with the furnace’s blower wheel. If you hear this noise, turn off your furnace ASAP and call a professional for help. 

This can be a problem with the blower wheel

  • The blower wheel came loose from the motor shaft and is now hitting the blower casing. If the wheel or shaft isn’t too damaged, a professional can tighten the wheel.
  • The blower wheel is broken and needs to be professionally replaced.
  • The motor mount broke, causing the whole blower assembly to drop and hit the housing

Loud Bang When your Furnace Turns Onfurnace repair, slinger, heating contractors

  • Dirty furnace burners – the dirt on the furnace burners delay the burners from igniting, causing an excess of gas to build up. So when the gas does finally ignite, you’ll hear a loud bang. You should never ignore this noise because these small explosions could crack the heat exchanger (which is expensive to repair). Regular furnace maintenance can help prevent this issue before the heating season even starts.
  • Expanding and contracting air ducts – this is a common noise for homeowners with metal ducts. The ducts expand and contract as the blower turns off and on. This could be a sign of undersized ducts, closed vents, flimsy ducts, or a clogged air filter.


If your furnace rattles or bangs loudly for about 30 seconds before the blower kicks in, your heat exchanger may have developed a crack. A cracked heat exchanger can cause carbon monoxide to enter your ductwork, and you should get it fixed immediately. Children’s toys and other small objects can make their way into the recirculation system and get sucked into the fan box where they bounce and rattle around.

Start-Up Sounds

If your furnace starts with a loud “whomp or Bang,” the air to fuel mixture is likely wrong or your ignition is delayed. If your furnace hums or roars loudly when it starts, the inducer motor is probably bad. If your gas furnace clicks when you start it, the flame condenser might be dirty. If your furnace howls loudly when it kicks on, your heat exchanger might be cracked. You should get that fixed immediately because it can leak dangerous carbon monoxide. 
Horsch & Miller Plumbing and Heating serves Slinger, Jackson, Milwaukee And surrounding areas with full service Emergency repairs and Furnace Replacements. Service when you need it, with competitive pricing. We will send you a qualified technician, not a salesman, who knows how to complete his task within a minimum amount of time. Whatever and whenever you need us