I have a 10 year old propane forced air furnace in a 10 year old house. Sometimes, but not always, when the blower comes on to heat, I also hear a loud buzz for perhaps a second or two, but sometimes for as long as 10-15 seconds. Otherwise everything seems normal. What might be wrong?

Is the blower actually working or turning at the time of the buzzing ? Or is it just trying to start up,maybe you could turn it off at the stat and be right at the furnace when someone turns the stat back on and tell where the noise is comeing from exactly

The blower actually starts along with the buzz.

I just tried twice while at the furnace to try to determine where the buzz comes from, but both times operation was normal, with no buzz.