I have a few questions and comments about this...
Did you try another outlet (without the panamax)?
Is the unit in close proximity to anything else?

If you are serious about the sound, a dedicated circuit is a GREAT investment. I put one in myself before I got my units, so I do not know what they sound like without it. I do not use a power conditioner, just an inexpensive surge protector (read power strip). I had thoughts of buying one before I heard the system, but it is dead silent, so I didn't want to mess that up.

The reason that I asked the first question is because there is one circuit (room) in my house that buzzes any equipment I plug in (guitar amp, stereo). I suspect a bad ground, but have not fully investigated. This is isolated only to that room.

Also, your panamax should not report a ground fault for a faulty ground.