I agree with sbank....its a ground problem. If you use a cheater, only use it to confirm a ground issue...don’t keep it in the system....they ruin the sound. Use a voltmeter to see that all wall plugs are wired correctly. This can be very tricky to find. I would get in touch with both Phoenix, and VPI and see if they have suggestions. If I were in a betting mood, I would say that Harry has the answer.
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?