Why humming noise from variable frequency drive (VFD) driven motor. Why is it so? If the application is not demanding you can "regulate" the sound and its pitch. Get into the VFD parameters and find "carrier frequency". Typical values are about 2-15 kHz. Then set it to 2 kHz and run the motor - if you have a musician ear - note the noise. Then go back and set 4 kHz and repeat the procedure +++ until you run the motor on max. kHz carrier. Have you noticed the change in the hum noise? Remember that you are not running the motor anymore on heavenly beautiful sinusoidal signal. You are running it on bunch of ugly pulses. To do this you have to cheat the motor (feeding it with crap) and this is done rather successfully because any motor constitutes an inductive load, which means, it is resisting the rapid signal change, averaging what was given to it.