Furnaces make noise, no question about it. The gas burner itself makes some noise. When the motor start it also makes noise. The air circulating can make some noise as well. Having said that if your furnace is making too much noise then something is clearly off or wrong.
If the noise level of your furnace has gotten higher, listen to the furnace while it is on, and see if you can isolate where the noises are coming from. If you suspect the noises are coming from the burner in the furnace, then you should call a furnace expert immediately. While the furnace is running, listen to the noises you hear and try to pin-point where they are coming from. Some possible causes follow.
Noise in the blower(fan) box.
Junk in the fan box -
If you suspect this, stop the furnace and open up the fan box. It can happen where small objects start off by getting into the recirculation system and then eventually get pulled into the fan box. At this point they can bang around in the blower and makes a lot of noise. An example might a children’s toy. If an object has made its way to the blower then there must be holes in the filters to have allowed the object in so they will have to be replaced.
If you are familiar with it, check the fan blower cage to make sure it is not damaged. Spin the cage with your hands and if resists, does not spin easily or is wobbly, then we strongly suggest you consult with a furnace expert or technician.
Loose or broken fan belts.
Loose belts-
Similar to a car, loose belt can cause a squealing noise when the first turns on. If the fan belts are particularly loose, you may also smell burning rubber. If you’ve heard the noise or smelled the fan belts then you need tot get those belts replaced. We recommend a furnace technician.
It is possible a damaged or jammed fan blower cage can cause the belts to squeal when the motor first starts. A furnace technician can make this determination.
Broken fan belts-
It can happen that a fan belt can be damaged but not completely break all the way. It can then flap around against the housing of the blower and make a tremendous racket. If you suspect this then turn off the fan and remove and replace the damaged fan belt. A professional can certainly help you with this. He can also check for any other damage the broken or frayed belt may have caused.