If your dryer is making a loud growling noise and sometimes buzzes when the start button is pushed or sometimes the motor shuts off before the cycle is completed then you may have a problem with the motor.
Always remember to clean the dryer lint filter after each load and it is helpful to keep lint from covering the motor which could cause it to overheat and burn out.
If the dryer is humming after pressing the start button and you cannot turn the drum by hand it is likely your motor has burned out and will need to be replaced.
Caution: Always remove/disconnect the power source from the unit you are working on. Unplug it! When unplugging or removing the power source, double check to make sure you removed the proper cord or turned off the proper breaker.
Check to see if the motor will rotate freely and run it with the belt removed and blower in place. If the motor runs good without the belt then the problem maybe the idler pully or drum. If the drum cannot rotate fully with the belt on, you may need to replace one or possibly both of these parts. If you have to hold the start button down for a couple of seconds, this is most likely the sign of a burned out or bad motor which will need to be replaced.
If your dryer will start but then stops after just a few minutes then your problem maybe a malfunctioning thermal overload detector which is mounted on the motor and heater box.
Perhaps the motor hums but does not rotate even with the belt removed, but you can still turn the drum by hand, you may have to replace the motor or motor start capacitor.