My furnace makes a popping noise when it shuts off. I tried changing the filter but it still makes the noise. Why is it doing this and how much will it cost to have it fixed?

I may or may not be able to help with some more details. Does it seem to be coming from the blower compartment since you changed the air filter? Or is it more of a sharp pop coming from the combustion chamber? Even if you sent me a sound file, I might not know enough to open it. Does it come when the gas shuts off or later when the blower goes off? If I figure out what it is, I still may have no clue how much it would cost since I never pay anybody to do repair work for me.

Is it poping or a bang? My system bangs when the blower shuts off. It's the return duct going back to normal from the "suction" pressure of the fan.

If you have a metal frame around your filter it is very possible that when the furnace blower comes on it lifts the filter up against the blower housing then when the furnace blower go off the filter falls and the metal frame hit against the matal base of the furnace making the bang. If this happens to be the problem you can stop it by laying something small but still heavy enough to keep the filter from raising up, or you could cut a piece of packing foam thick enough to put between the filter and the blower housing, make is snug enough that it will now easily pull out.

As far as cost, if this is the problem I would think that an honest repair man would charge you a service call, which could change drasticly according to the area you live in.

Let me know if this was the problem