As someone mentioned, it is probably the belt, or one of the black
rubber-type rollers at the rear of the drum, or possibly, though it
does not sound like it, the idler pulley.

Dryer repair is pretty straight forward. The typical "reader's
Digest-type" home repair book at your local library has detailed
troubleshooting charts and repair instructions, photos.

I'd pull the front off, have the wife help by holding the drum and then
turn the thing while it is open. By looking and listening, you can
probably isolate the source. Lint trap seems a pretty far-out
possibility here, but then again, I guess anything is possible.