How does the noise manifest itself, i.e. from the outlets, from your amp, or from your speakers? Does it change when you increase the volume on your preamp or is the level always the same?
I have four Audio Prism "Quietline" plugged into various outlets around my house. i have two on the circuit that my equipment is plugged into and one on each of the other house circuits. They seem to work fine.
If you have a cable TV line near the wall plug unplug it and see if the noise goes away. You may also try grounding the cable line.
If you have t12 fluorescent lights with magnetic ballasts on the same circuit the will also inject noise in the line. Try converting to T8 with electronic ballast.
I have found using a Monster AV2000 gets rid of noise in the lines.
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