The fan is vibrating. What is wrong?
Several things can cause vibration. Before assuming the wheel is unbalanced, check other possible causes first. Look for any obvious signs of a rag or foreign object stuck in the wheel. Another common problem is the fan was recently cleaned and not all the grease was removed from the wheel causing it to be out of balance. Mechanical problems can be the motor, belt, bearings, or wheel. Remove the belt and run only the motor if it vibrates replace motor. Check the belt. If it is in poor condition replace. Make sure the blower pulley and the motor pulley are in alignment. Check bearings for wear or damage. They may also need lubrication. Finally make sure that the fan is secured to the curb. Just adding an extra screw can sometimes quite a noisy fan. If a fan is operating outside its performance range it will also vibrate.
