I had this on mine...in my case it was an easy fix.
Open the door, and try to lift the front top of the drum. If it moves more than just a little, it is probably in need of replacing one (or both) of the idler wheels. These are typically a hard rubber roller maybe 4" in diameter and 3/4" thick that support the drum. If you have a gas dryer, the one on the side next to the exhaust tends to get the bronze bearing messed up after time. If you can move the drum, take the covers off and check. The idler should rotate freely without any wobble. You might want to buy a new shaft as well for the roller if that is the case. If that is the problem, the part is (or was, I replaced mine maybe 8 years ago) only about $8.
If that isn't it, somebody else may have some other suggestions. My unprofessional opinion.