Hunting down hum is a pain in the Arse. I get random buzzing in my own system, haven't heard it in a while, but I did have to call the power company about my lights flickering and since then, the hum has been gone. My projector had an issue inducing Hum when its HDMI was plugged in, I wound up using a device to lift the ground.

For you, try connecting both racks to the same circuit with an extension cord to try to eliminate the phase issue. is there hum without the interconnects attached? stupid question (may have been answered) but tells a lot.

You have satellite and cable? does disconnecting one or the other or both make a difference?

usually for hum, I start by disconnecting things one at a time and see what is the biggest cause and work backwards.

If you have any grounded power cords, try a cheater plug to see if there is any culprit.

I love these guys, have saved me a ton of headaches.

[Link: ebtechaudio.com]