Phoenix Engineering speed control

I purchased the Phoenix Engineering speed control for my VPI Classic 3. I purchased  the bigger power supply and the tachometer combination of the speed control.  I notice that I can hear a steady hum coming from the speakers when the speed control us turned. The hum is constant and will not vary if I turn up the volume on the Preamp.  But the hum goes away when I turn the turntable off. The hum return when I turn on the turntable again. I even in unplugged the interconnect from the turntable, but it make no difference.  Does anyone with the Phoenix Engineering speed control experiencing the same issue?