Dryer motors should be serviced when they show signs that their bearings are wearing out. A dryer motor features a small pulley containing one or more bearings. The small beads turn the pulleys connected to the motor and the drum. As time goes by, dryer bearings dry out and warp.
If a dryer makes a squealing sound when it runs, it is a sign that the motor bearings are starting to go bad. Bearings that have lost their lubrication make noise as they move. They may also squeak in a rhythm when the drum of the dryer turns. The motor might quit running and start buzzing after it heats up, and it might start and stop after several cycles. Any of these signs means it is time to have the dryer motor checked.