Hey all, Furnace Rookie here.
I just moved into a 30 year old house with a 17 year old thermopride 80%
efficiency 80k btu furnace.

Got my first heating bill back for December, 300 bucks, OUCH! is that
typical? I'm in SE Michigan.

Here is my question though. When the furnace cycles on, it starts up
normally, and runs fine, hot air at the vents ect.
however, when the gas shuts of mid cycle and the blower fan continues to
run, the furnace makes a clicking noise kind of like the sound that old
baseball cards made when put in the spokes of your bike.
this clicking slows down, and then stops, all the while the blower fan
continues to run without making a sound.

I opened the main panel of the furnace, and it looks like there is a second
smaller electric fan in there? The furnace vents thru a 4 or maybe 5 inch
steel pipe up the chimney.
Its sounds to me like there is a second fan (or something else that is
spinning) that runs when the gas is burning, and stops when the gas shuts
off.

Thanks for your help

Dave