Ground Hum, Help

[hazbin]

So I just did a jam with my current rack set up this weekend:
Mesa Mark IV Rack Mount
Mesa Road King
GCX Audio switcher
Rocktron Xpression
Chandler Power Conditioner
DMC GCx Ground Control

I am having major ground hum when the RK is connected to the GCX When I run direct to the RK, no problem When I play through the rack set up without the RK, no problem. When the RK is connected to the GCX even with the power off, MAJOR BUZZ HUM.

Looking for some help!!

 

[Aart]

use a cable with the shielding/ground attached to only one jack of the cable between the roadking and the gcx.

 

[Boltino]

You can try isolating the GCX from the rack using Humfrees or equivalent.

Or you can lift the ground from the GCX chassis internally. I was having a hum issue with a stompbox and was instructed to open the GCX up and disconnect the additional chassis ground. It's very obvious once you get inside, it's a wire connected to a green screw.