The drum is supported, at the front, by the round door frame itself, and on the back side, it rides on nylon rollers. I think the rollers have worn out of round. A worn drive belt will make the same noise.
Post back to me, if you want further assistance.
Remove the back cover to get access to the rollers. Replace the belt, which can usually be accomplished from the back also.
restaurant equipment technician
20+ years experience. I'm now employed at a central kitchen, which serves 5 restaurants.