Freemand I assume you've tried using XLR connections if possible with your pre. Keeping the power cords away from the cables, checked your power quality, or used or quit using a power cleaner device. Have you tried a different processor? Digital cable or sat boxes are notorius causes.
Really just a chore though of stripping down to the basics and working backwards through the system to isolate the problem. Remember to actually remove components when testing, still connected in any way can be enough to cause a loop.
I haven't just heard a Gemstone I bought one. I don't see a point in paying 6k+ to get something that may not be any better than this one for well under $3k. I talked with Steve on the phone - he called me, wanting to make sure this was the right amp for me - for almost an hour the day I gave him my credit card info. We had exchanged emails prior to this. Not the quickest responses ever and often get voice mail but these guys will advise to get something else if they think it's in your best interest.
