It was the combustion fan all along. I never listened for the noise with the side panels off and it seemed to be the convection fan. When I opened the panel on the side with the combustion fan I could hear the noise coming directly from the end of the rotor shaft. When the noise started again, I put a couple of drops of 3-in-one oil on the end of the combustion fan and the noise stopped instantly. And, I'm getting a better flame.
I sill have the old combustion fan if it ever comes to that.