Thumping noise when drying

I removed the 2 screws under the lint cover and popped the top of the dryer up and back. I then unplugged the safety switch wire on the upper right of the front cover. Next I removed the 2 screws holding the front panel on and popped it off while supporting the drum. I took the drum out after taking the belt off it. One of the rollers had the rubber stripped off it. This was kind of curious since I put in a full kit including belt and rollers a few months ago. I replaced the damaged roller and reassembled. I will save the second roller in case it happens again. There is no apparent damage to the drum so I have no idea why the previous roller didnt last.