During generator running time, all Heavy Ac motors were making the humming noise in motors but this is not happening in EB supply. Where is the problem?

Please check the frequency (Hz) of the Generator. It suppose to be 50Hz. If there is any difference in speed of the generator due to electrical load or improper setting of the speed of the Generator the frequency will vary. Also check the difference between the EB voltage and the Gererated voltage. By collecting all these data you could able to conclude the solution.

Check out the following points.
1.Check the frequency cycle,It should be 50 Hz or 60 Hz.
2.There should not be any huntting in the generator
3.The voltage should be constant .
4.Check the Automatic voltage regulator for its performance... If malfunctioing then replace
5.If the DG is running in synchronising mode then maintain the synchronising parameters or check each DG individually for its performance.
6.Check the diodes
7.Finally the phase sequence & I hope you would have done that