Help with AC noise please

Hi all, I have a dedicated AC line for my audio, Monster 5100 filter, Quantum symphony conditioner, Nordost Red Dawn interconnects, MIT T2 biwire cables(15'), MF cdpre24, PS audio amp, MF tube buffer, Emminent Tech speakers,
When I put ear close to the speakers I can hear what sounds like something frying in a pan, sort of a crackling sound. It is louder through the left speaker than the right. To make things worse for about two days the left speaker was absolutely silent, with the right speaker only emitting the noise very lightly. I have removed, and relocated all the devices but when the noise is present it stays. I tried rerouting the cable, even lifting them up off the concrete basement floor, but no help. I unplugged the tube buffer, no help. All the equipment is mounted on a verticl rack. I have moved the tube buffer away from the rack. Even with all the lights out I still have it. But then sometimes I don't. When the noise is gone I tried to discern what was different but could not. Does anyone have any ideas? Thanks