Your home's furnace will never be perfectly silent, but the noises should be mild so that they fade into the background sounds of your home. If you are hearing loud, alarming sounds, you will need to find the cause and have it repaired.
Is the Blower Assembly Damaged or Loose?
Odd noises are often a result of damage inside the blower assembly. The simplest to fix is the rattling noise caused by a loose fan blade, as this usually only requires that a screw is tightened. More insistent thumping or rattling noises can be indicative of a loose fan motor mount, which will need to be replaced before the fan shakes loose completely. Thumping and vibration issues can also be caused by loose mounts, but often these noises stem from an out of balance fan. Your heating repair technician can rebalance the fan and fix the problem.
When Was the Last Time the Unit Was Serviced?
Dirty belts and moving parts can also lead to squeals and rattling noises. Dust and dirt on a belt can be quite noisy. You will likely hear the noise from belts when the blower first starts up. Loose debris attached to the blower fan can make rattling noises the entire time the blower is running. Squeals and squeaks can also be the result of poor lubrication. The moving parts in your furnace need to be lubricated annually so they run smoothly. When they aren't lubricated, the chances of friction damage increases as does the chance of a breakdown.
Are the Vents Open and Filters Clean?
Poor air flow into the and through the furnace can lead to popping or loud banging noises. If these noises are minimal and mainly only occur right as the furnace comes on, they may simply be from the ductwork flexing as the hot air hits them. If they are more consistent and loud, then the filters may be dirty and blocked up so air isn't flowing properly into the furnace. Fortunately, you can repair this issue by replacing the filter then having the entire furnace cleaned to remove dust. Blocked vents and air returns can also minimize air flow throughout the furnace and lead to banging sounds. Open all vents and make sure there are no obstructions if you want to fix the issue.
Contact a heating repair service in your area for more help with your noisy furnace.