I haven't tried every PWM frequency, but I have tried about a dozen.
They all whine until I get up to 16kHz, where I don't hear it. This
would be fine except that above 12kHz the drive is only rated at 80%
(2.4HP); I intended to run a 3HP motor with it.

I believe that high switching frequencies are hard on the motor.
Particulary if the motor is not designed to be used on VFDs.