WOW !! Am I ever glad I walked into the garage this morning !!! My overhead heater has been working effortlessly for the last 20 odd years !!! Then this morning when I was in there, it kicked in but I did not hear the fan blowing - rather a HUM !!! Thought I better check things out . . . turned off the furnace (this is a hanging off the rafters type gas heater with fan) . . . after all this time, the fan blade had "walked" back on the motor shaft and then when it went to turn, caught on the fan guard !!! . . . I was lucky, no motor burn up, because I was there to shut things off right away . . . anyhow, pulled off the fan/motor/guard, and the fan blade screw to the motor shaft was tight, but I loosened it and moved fan blade back to it's original position, tightened the screw, reinstalled and voila, furnace working 100% !!!
Just a call out to everyone, check your furnace, at least more than once in 20 years !!!!