Mike,

Sorry to be so long in replying. There is something WRONG with your K2600. You state that you hear this both with digital out and analog ..

I suspect you have a hardware problem.
I can't tell you what (not a tech)

do any other sounds "buzz" .. check carefully..
(I suspect they do if you really listen.

A repair is definately in order. before taking it in...

Download the latest OS and Objects and reinstall it and then do a hard reset.. If the sound still "buzzes"

take it in for repair or make sure your House "Sync" is working properly..

BTW..

Here are the names of the new voices for the K2600 family. the sounds for GM 400-500 are for the K2661

http://www.geosyncmusic.com/K2661Pgm/K2661Lst.htm