Furnaces—especially older models—often make noises. Normal sounds are minor pops from the ducts and the humming of the furnace as the blower runs. Ignoring these noises would be a big mistake since what’s causing them could lead to even more costly repairs (or even costlier replacement) later on.
Loud Scraping (Metal Rubbing Metal) 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 us for help.
Loud Bang or Pop When the Furnace Turns On
Bangs or pops are usually caused by one of these two reasons:
- 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.
Squealing or Whining Noise
This squealing or whining noise isn’t as big of a deal as the others listed above, but it’s best to get it fixed before it causes any further troubles inside your furnace. An annual furnace maintenance visit every fall can prevent the belt from getting too loose or certain parts from being under-lubricated.
Call a Professional to Make Sure
Even if the strange noise is minor right now, that does not mean you shouldn’t get it checked out because it could snowball into a much larger (and therefore costlier) problem later on.