Does the motor swing around?
The rotation must be oscillating, and the motor will also produce the left and right swings of the left and right sides
The motor bearing is out of question, causing the left and right oscillation.I hope my answer will help you.
First can tear down load belt try, if still swinging, that is the motor is out of the problem to see not fixed, or the inside of the bearing looseness, if there is something wrong with the bearing should be supposed to send sound or with fixed load. If you put a belt on it, it's probably a belt that's not tuned and you can figure out how to do it.
