The Vibration motors are quite different from the conventional induction motors. They are built with a unique design concept to generate centrifugal force . The centrifugal forces are generated by the rotary motion of the unbalanced masses on the extended shaft.
When a motor is running with load if it is delivering abnormal sound due to vibrations can be observed.
Generally motor vibration takes place due to the wear and tear problem, if bearings are worn-out, if base mounting bolts are loosened and sometimes it so happens that cooling fan becomes loose and touches to the end Shield of the motor and vibration and sound can be observed.
If V belts are loosened motor vibrates. To overcome this problem we have to analyse after seeing it practically on the load condition.