Ground Loop Problem - Stumped

I Haven't the time right now to read all the responses, so forgive me if this has already been addressed. The hum you describe is likely 120hz(full wave rectified 60hz line freq) picked up from the power supply. The difference in voltage drops between your two grounds,the innterconnects, and the power cords,cause this noise. If only one power ground,generally at the preamp, is used ground loops can be avoided. HOWEVER, if the interconnects come off you gots an ungrounded piece of equipment. Not good.

Are you sure your interconnects are good? You may want to get a meter and check continuity.

Try grounding your amplifier to your preamp. You would need to losen a screw that attaches to the frame of your amp and preamp and attach a ground wire. I have the same problem and talked with John Bayloff @ Theta the other day and that is what he recommends to do. He suggest maybe doing it at the feet of the unit. I have a Meridian 568.2 and Theta Dreadnaught. It only occurs on the rca interconnects for the surrounds as I use balance cables for the L/C/R channels. I imagine that your EAD amp is balanced and the RCA cable is unbalanced only which creates the 60 hz ground loop. Good Luck

Thanks for all the responses. Sorry for not following up, I've been swamped at work and haven't had a chance to enjoy my audio system. Okay, I will answer each of the questions:

1. Plugging the map directly into the wall does not alleviate the problem. I still get the hum.

2. Plugging each of the ExactPower units into the wall rather than into one another does not fix the problem.

3. I have not tried an isolation transformer between my amp and preamp.

4. My system is connect to cable TV. I have disconnected all the cable TV connections and the problem still persists.
It is important to note that this occurs with everything else disconnected and unplugged from the outlet. All I need is the amp and pramp connected and powered on and connected to the speakers.

5. I don't know if it's a ground loop or a 60Hz pickup on an input. One interesting thing is that I just got some Odyssey Mono Amps and when using those to drive my main speakers I don't get a hum at all from the main speakers. I still get the hum from the center and surrounds though that are connected to the EAD amp.

6. I've tried plugging everything into just one of the ExactPower units and the problem is still there.

7. I have tried 3 different pairs/brands of interconnects and the problem persists.

So it seems odd to me that with another map I don't see this problem. Could it be a problem with the amp? If so, how do I go about diagnosing what the problem is if any before I ship this beast to be serviced/checked out.

Thanks again to all who replied.

What G68 are you trying to get to work? If it is the XLR 'balanced' output version ("G68XXV")and you are using truly balanced interconnects into a truly balanced amp input, then this may be the problem. I have heard the rumor that the XLR connectors are NOT configured by Meridian in a balanced manner and so a balanced interconnect does not work properly. I am currently investigating with Meridian and will keep you posted.