If you recognize the user-ID, then you know the problem I'm about to describe because I've been yapping about it in these forums, on and off, for *years*. I'm only in here to try again because everything I've done so far to try to fix it has resulted in just more credit-card bills.
The sound is perfect for the first twenty or thirty minutes -- always has been, and I always think I've fixed whatever's wrong -- and then, gradually, the sound becomes reedy and increasingly sibilant in the upper midrange and apparently "over-modulated" right around the midrange-tweeter crossover.
If I shut everything off and reconnect everything, the problem often goes away for another twenty or thirty minutes, but not always.
It can't be a problem with components or speakers because everything in the chain has been repeatedly replaced, and many configurations have been sent off for service and returned with clean bills of health.
I don't think it's RF pollution because I've encountered the problem at a friend's house, and fixed it doing the same thing, over there: reconnected everything and had great sound for... twenty minutes.
I don't think it's a cracked RCA input socket because the problem has spanned several configurations of equipment.
I don't think it's a bad interconnect because the problem has spanned several configurations of cabling.
I don't think I'm delusional because non-audiophile listeners have commented on both the unpleasantness of the sound before reconnection, and the improvement afterward.
At all events, something seems to be "building up" in the signal path, somewhere, and the act of severing all the connections seems to cause whatever that build-up is, to be dissipated.
Lately I've been trying to fix this by... well... *reading* -- about everything from PS-Audio Humbusters to Audience Adept Response power conditioners and back to the XDC power filters by Channel Islands Audio. Trouble is, I'm cleaned-out financially and I just really don't feel like spending any more money before knowing with a bit more certainty that more dollars spent will point me more definitively toward getting to the bottom of this. Are there professionals who can help to diagnose the problem, and who are then also knowledgeable enough about the industry to recommend the proper fix?
Current system configuration: (many, many others have been tried!)
McCormack MAP-1 and DNA-HT5, connected directly to dedicated AC circuit via Signal Cable power cords
Arcam FMJ-CD23 connected directly to nearby, undedicated AC circuit, via signal cable digital power cord
Sony BDP-S550 blu-ray player and Panasonic TX50 plasma TV, connected to APC H-15 power supply, which is in turn connected to the undedicated AC circuit via Harmony power cord
Salk Songtower QWT speakers, front L and R, Linn Trikan center channel, Totem Mite-T rear L and R.
signal cable interconnects, element cable cross-connected speaker cables.
Thanks again, everybody.