Furnace has taken to "chirping" -- sound of two pieces of metal rubbing against each other. Traced to one (?) of the removable door panels (*probably* rubbing on the OTHER door panel!).
As this panel covers the combustion area, flame is nearby. Heat is to be expected!
My initial thought (when I thought it was the *blower* area door) was to put some self-adhesive "felt" on one of the offending surfaces (the "fuzzy" half of some velcro). But, not too eager to try that with the presence of flame.
Any other suggestions?
I'll pull the blower out this weekend and check to see if it's got a balance problem (bad bushing/bearing?) leading to any possible increase in vibration (nothing obvious).