What does this tell me?

Sounds like it could be a grounding issue. Please give details on the circuit you have this connected to, if there is anything else connected on the same circuit in the room (lights, dimmer switches, power-blocks for computers, cellphone charging, etc...). what are you using for a pre-amp or processor, i.e., what's everything connected to? Have you had an electrician check that the outlets on the circuit are wired and grounded correctly?

Try process of elimination. Unhook all sources that you mention and install them one at a time until you find what is causing it.

It's a dedicated 20 amp circuit, with two outlets about 8 feet apart. It was
installed by my dad, who is an electrician.

One outlet has a TRL power strip plugged into it. Into the Power strip is the
Squeezebox, Oppo DVD player and Behringer DEQ. I have a Krell integrated
plugged straight into the wall.

The other outlet has Power Wedge power conditioner plugged into it. Into
that conditioner is a plasma tv, satellite receiver and sometimes a playstation.

I also have a Vandersteen sub plugged straight into the second outlet.

Besides the other good suggestions which have been offered, I'd suggest that you try unplugging the Power Wedge (and therefore everything that is plugged into it), and also try plugging both the Krell integrated and the Vandersteen sub into the TRL power strip (assuming it has sufficient current-handling capability).

Both the plasma tv and the satellite receiver could be generating rf interference that may be coupling into the low level components. The problem could also be worsened or caused by ground offsets (differences in potential) between the different outlets, or resulting from having some things on the conditioner and some things not on the conditioner.

Also, I'd suggest taking a portable am radio, tuning it to the bottom of the band (around 550kHz), and walking around with it in the area of the system to see if it picks up significant rf interference. As was mentioned, both dimmer switches and compact fluorescent lighting (or full-size fluorescents, for that matter) can be potent rfi generators, especially if the fluorescents are nearing the point of failure.

Hope that helps,
-- Al

Does your interconnects or speaker wire run across any power cords? This happened to me when I had the Odyssey Stratos amps in my system.