Product review (5 stars): Dryer Roller Kit
Perfect fit.  Works with many brands and models.  Includes two wheels and two axles.  To install: pry up the top of the dryer.  Disconnect the door switch.  Remove the front of the dryer.  Remove the drum belt.  Pull the drum out.  Pry retaining clip off with a flat head screwdriver.  Remove wheel.  If you need to replace the axle, there are two screws to remove.  Easy and cheap fix for a loud/thumping dryer.