How to isolate culprit in buzzing speakers?

recently began auditioning a friend's PS Audio-600 power plant. was amazed by the overall sonic improvement to my rather modest system. despite the musical upgrade, i noticed a bizarre, audible, pulsing-buzz coming from inside my amp. after some trouble shooting with PS tech support we traced it back to surges in the PS-600 and sent the unit back to be serviced.

knowing what it could sound like with the PS - i had no desire to listen to my stuff while waiting on the repair. when it did return - i plugged all my gear back into the PS-600. fired everything up and now heard a rather loud buzzing coming this time from both speakers.

i'm troubled because my system does not sound nearly as good as i have heard it in the past {either with or without PS-600}. been considering upgrading my amp, wiring and perhaps speakers to gain more musicality. but, something tells me i should hold off until i get to the bottom of this annoying problem. what say you?

what steps can i take to isolate the culprit? could the 'surges' from the 600 have anything to do with my gear sounding off?

current system:

power plant: PS Audio PS-600
pre-amp: Audio Research LS3
cd: Naim CD5i
amp: Rotel RB 981 {120 wpc}
speakers: Paradigm Studio 100's V3.
speaker cables: Transparent "The Wave"
interconnects: Interlink "The Link" 200

thanks in advance,
timothy