I just want to share my experience with my fellow audiogon. I have major ground loop problems even with a new electrical main panel and multiple ground rods and ground to the main water line. I use the Ebtech Hum X Ground Line Voltage Filter which can be bought on Amazon for $79. This Ebtech Hum X can also be found on Musician’s Friend, Guitar Center, etc. I use 3 Hum X on my 3 amps which work wonders. Btw, I also have RGPC Substations & 600S & 400S, Shunyata Hydra V-Ray & Hydra 8. Only the Ebtech Hum X works with eliminating the ground loop hum. You can always return it if it doesn’t work in your system.
Good luck,
Tuan
Good luck,
Tuan