In my battle to fight the noise coming from my rig, 1 of the main culprits I've pinpointed is my compressor from Keeley. For the record, i think its the best compressor (that I can afford that is). I still keep it in my rig regardless of the noise. I even bought the voodoolab pp2+ hoping to solve some noise issues (blame my p90s as well). So are compressors generally noisy? I like to keep the Sustain knob above 9o'clock and work my way around the noise problem.