Abnormal noise in 2pole motor at less speed

[Shiv2010]

This induction motor is working fine at 3000rpm, however giving abnormal noise in between 2000 and 2300 rpm. Can some one suggest why and solution ?

 

[maripali]

Suggest, that critical velocity of the rotor is between 2000 and 2300 rpm.
When bearings have a loose the rotor starts to vibrate and gives that noise.

 

[Tmoose]

I'd say much more information is required for a useful answer.
The nature of the noise, the history of the motor's service, and the history of the "noise", any troubleshooting of the VFD, pictures and drawings of the installation.