Jazz, I'm not sure to understand what you are saying... will the ESS fix the issue IF it is a ground loop going to the PC ?

I have tried getting rid of the ribbon cable. Same problem, though I had disconnected the X axis motors because I didn't want to twist the gantry. But then it was a little more difficult to hear the noise but it was still there. I will do some more tests on Thursday, I'll connect everything back together to get the maximum noise, then disconnect the DB25 cable and see if that stops it. I'll let you guys know ASAP.