Leslie project....

Hi, I was just wondering if it is possible to eliminate the audible motor noise that’s produced when a standard DC motor is driven by PWM. I’ve used different frequency to drive the PWM but all seam to have some audible squeal at mid to lower speeds.
I would like to drive a standard DC motor, one direction at two diferent speeds for a Leslie speaker project, and of course the noise is unacceptable.
Am I better off looking into an adjustable voltage circuit, as apposed to PWM to solve the noise issue?
Any references to such a circuit would be appreciated.

Thankx