The buzzing is clearly in the piano programs themselves. There is a good thread at the Yahoo K2600 User Group in which Stoph describes how he modified Piano Program 1 to eliminate most of the problem. Specifically, see post 1751 (and the rest of the thread): http://groups.yahoo.com/group/Kurzweil-K2600/message/1751

Subsequently he was also able to greatly reduce the problem in a Sweetwater Grand Piano program.

I am absolutely amazed that this hasn't been a big issue with users of the piano programs. The buzzing is very evident if you listen for it. Several K2600 User Group members agreed they had noticed it, but they have simply lived with it. Kurzweil and Sweetwater need to modify their programs to reduce the problem, using Stoph's approach. Stoph did it relatively quickly (though he is experienced at modifying the programs). However, I have had no luck getting their attention.

Mike