When I described the noise to a YouTube appliance diagnostician, I was directed to check the felt seals front and back of the rotating drum for wear, tears, or foreign objects. As it happens the felt seals looked find and there were foreign objects so, not wanting to disassemble and reassemble the dryer more than I had, I ended up replacing all the replaceable moving parts that I considered possible culprits: The idler tension spring, the idler tension bracket (which includes a nylon pulley wheel), the drum belt, the five rubber-tipped bearings that support the drum and keep it in place, and the foam seal on the blower housing which seemed a little brittle and old, as well as high-temperature adhesive for the latter. The instructional videos here and on YouTube were extremely helpful (I doubt that I would have attempted this job at all, had I not watched these ahead of time). The most time-consuming aspect was waiting for the arrival of the parts as I didn't order them all at the same time or all from the same place (I ordered from whomever could ship me a given part the fastest. Disassembly took less than an hour. Re-assembly with the new parts in place took about the same but was a little more awkward because this appliance sits in a very narrow closet and it's difficult to ensure that the 4" flexible duct stays in place when sliding the appliance back into the closet. No regrets. Now I know the basics if this dryer needs attention in future and I also know all the parts that I can eliminate as suspects in any future maintenance (the parts that I replaced)