Take a look inside the dryer and with a torch look at the panel in the middle of the drum at the back. There are three rivets which hold the drum to the bearing kit. The rivets may have moved and the noise you are hearing is the loosely fitting drum moving on the rear bearing fixing mount. You will see the rivet holes may have stretched. As far as I know you would have to replace the drum to fix this issue. Other causes could be the fittings at rear of tumble dryer loosening and allowing drum to move. Sometimes the belt may have become worn and is moving towards the back of the drum. The drum should be replaced if it is losing its shape. Good luck.
Rockdrive, November 2014
