On Sun, 10 Apr 2005 17:12:48 -0400, Bob Engelhardt
wrote:

R. O'Brian wrote:
The motor is the problem. ...

I'm certainly no expert, but I have a little direct experience with
this. I have a 3 ph motor and VFD on my drill press. It is the 2nd
VFD. The first one sang, this one does not. Same motor, same wiring.

Bob

The Mitsubishi drives I have at home allow modification of the PWM
frequency. Allen-Bradley drives I use at work do as well. Changing
this frequency may reduce the noise generation, particularly if it
moves away from a mechanical harmonic frequency.

Pete Keillor