You need to open the top and see if perhaps a piece of the black mastic is hitting the cabinet or something is stuck to the grooves where the rollers ride at front and rear edges of drum. Pull your filter out and remove the 2 screws that are under it. There are also 2 clips (probably plastic) on the front edge that may be more fun. They can be compressed with thin putty knife or other similar object but I usually pull the whole top forward and it will clear the clips if you are lucky. You can run it with the lid lifted, just take care not to get anything caught if you lean over it. You can turn it by hand at first to avoid running it at speed.

If nothing there you may have a damaged belt as it rotates at close to drum speed.Rollers are small and so spin much faster so the repetition of the thump would usually be faster.