this is a common problem on dryers, it sounds like one of the idler wheels has worn out, they sell a stud and wheel kit that is very cheap, under $5.
you have to pop the front of the dryer off i used a flat bladed scraper to do mine, take the belt off the idler pulley, that pulley is near the motor. then the drum will pull out toward you.
at the back are two black wheels one or both of those are bad.
when i did mine i replaced the belt and the idler pulley for the belt as well as the drum wheels
the hardest part of the job is getting the darn front off, two clips on the top and bolts at the bottom
good luck and feel free to pm me if i can help