Strange noise in furnace

I have a Williams natural gas, forced air wall unit; 10-12 yrs old. For about a week it has been making an occasional loud "riveting" (rapid staccato tapping) noise and seems to be coming from the upper part of the unit, even when not running. The noise only lasts a few seconds at a time, is quiet for a few minutes, then repeats - sometimes four or five times. This has been occuring in the early a.m. before I get up, when the thermostat is turned way down, but I have heard the noise even after I turn the thermostat up and the unit is running. The noise goes away during the day and is quiet until the next morning, and the furnace seems to be functioning just fine. The noise is similar to when a fan is off-balance and hitting the edge of its frame, but as I said this noise happens when the unit is not running (and it has NOT been windy here).

 

Awhile back I had a customer with the same problem exactly. checked everything. Found nothing. Her nieighber found out it was a woodpecker.

 

yep that's going to be it. Those pesky woodpeckers.

 

I can't believe it! Not even an hour after I read Kranky's post, I was out in the yard and heard the noise again . . . looked up on the roof and, sure enough - a woodpecker on the vent!! Blew me away. Thanks, guys . . . you saved me a service call

 

It's mating season. Woodpeckers "drum" to attrack a mate.

I'll never forget the first time a woodpecker (actually a Norther Flicker) started drumming on the metal chimney cap to my fireplace. I thought the Martians had landed.

 

and to think I was just being a smart ass...

 

That's funny, BuildPro . . . this has turned out to be rather entertaining. We hear the little guy every morning now, and it kind of warms my heart to think that he is courting from my rooftop