Try this tip, open the door, place your hand on the top of the drum and lift, if there is a lot of movement in the drum your bearings need replacing, if the drum is fine, check your belt sometimes when the drum heats up, if your belt has stretched it will make the belt too large and instead of pulling the drum round it will slip on the drum. Common fault with tumble driers, with the heat the belt will eventually stretch.
John atkinson
July 2010