One of the possibilities is an unwanted solid located between the coil core and the armature that is preventing the armature from travelling to its maximum extent.

thank u..!

Another possibility is that it is a DC coil and AC is being supplied to it.

Perhaps it likes the tune and just doesn't know the words.

Only if it is humming. If the shading ring is broken, for example, it will sound like heavy metal

It could also be an old contactor near its end of life. A few shorts in the windings cause excessive current and noise.

What is the rated coil voltage?

If the applied voltage is less than the rated voltage then there is possiblity of humming.

Please measure the voltage after giving supply to the contactor.

If there is dust then also humming is possible.

thank u all.... i found dust located in between coil core & armature core, after cleaning, it s working proper with out any sound....