Help with speaker buzz


Last month I purchased a new pair of subwoofer cables, I sent the cables back to the manufacturer for re-termination to RCA due to I purchased a new preamp that did not use XLR. The system played fine with the new cables in, however whenever I turned the preamp off I had a very loud speaker buzz and sub hum. I went through a process of chasing a ground loop with the technicians of the company, finally I had to send the cables back for repair, I inserted my old sub cables and the system was dead quiet on or off. Upon return of the new sub cables from repair I put in the cables played music all was well, however I turned off the preamp with amps on and the buzz came back but this time the buzz was much quieter and no sub hum this time around, I unhooked the active shield of the cable and the buzz went away. I failed to mention these are the top of the line Synergistic Sub cables. Can anyone help me diagnose this problem, has anyone out there experienced the same sort of problem. I am definitely at a lost. My system is on dedicated circuits however my subs are on house line, no cable tv or home theatre in my dedicated listening room if that helps any. I also disconnected all my direct tv sources throughout the house to see if I was getting feedback from a ground loop. I really like the sub cables, however I am on the verge of asking for my money back. Please Help

Thanks
Mitch
mmitch7711
always turn your amps off first...Amps last on- First off..
I never turn my amps off, with other sub cables in my system this has not been a problem. I don't think you read my post thoroughly to understand the problem I am having
"I turned off the preamp with amps on and the buzz came back but this time the buzz was much quieter and no sub hum this time around, I unhooked the active shield of the cable and the buzz went away"

Just from what you said, it would appear that something about the "active shield" is causing the problem. I'm assuming that you told Synergistic about your finding. I'm curious about what Synergistic had to say.

Another thing you might want to try, is take the sub off the "house circuit" and try it on your "dedicated circuit" and see what happens. I'm thinking that because you amp is on a "dedicated circuit" and that sub is on the "house circuit", that the sub cable (or active shield) may be acting like an antenna and picking the "buzzing" noise.
Yes I have told Synergistic about the problem, I even send them back a second time for troubleshooting. SR is adamant about a ground loop, another analogy was as Cleaneduphippy suggest that the active shield was acting like an antenna picking up a buzz. I spoke to one of the technicians where I purchased the Cary, as he is very familiar with the SLP-05, his answer was in line with the antenna theory, his suggestion was to leave the preamp in "mute" once I am finished listening for the day. I asked will this cause the tubes less life overall and his reply was "very little" as there is no signal being transmitted. He also suggested as Thorman said to turn the amp off, then preamp and I could turn my amps back on if I want to leave them on all the time, just ensure to turn off the amps before turning the preamps back on the next day. I guess this will be the route I will take from now on.

Thanks all for your replies