From jmkarns@yahoo.com Fri Oct 07 07:40:07 2011
Subject:Re: Pwer noise from laptop Audio out

I had this same problem and traced it to a Lexicon reverb unit that I was using with my Privia keyboard and HP laptop. By eliminating that one component the line noise was gone. Often these problems are as a result of poorly shield cables or inadequate grounding. Are there any surrounding devices giving off large abmounts of RF? e.g. monitors or florescent bulbs? I would use the process of elimination in your audio environment to try to find the culprit. (anyone else?)
Good Luck!