Could be something not letting the motor turn freely. Like lint jammed against the fan , tub bearing bad or needs grease . if the motor will turn freely by hand it could be a bad motor.winding .you could take the drum belt off the motor & see if the motor will run ok If it buzzes with the belt off pretty sure the motor is bad you would have to replace it . A motor is expensive so try to check everything to be sure it is bad. I have seen some that you could oil the motor shaft & it would help. If lint is keeping the motor from turning clean all the lint you can all through the dryer & the outside vent .If you check the motor with the belt off don't run it very long as it will get too hot . Hope this helps