For almost 3 years now I have dealt with a horrible buzzing noise emanating from the external speakers connected to my PowerBook when it was plugged in to things on my desk. At some point I discovered it was linked to having my 17″ Apple Studio Display plugged in, but leaving it disconnected kind of defeats the purpose, so I didn’t track the problem any further. So the magic is this; turn the brightness slider all the way up in the Displays control panel, and no more buzzing! It turns out that it is only the dimming of the backlight that introduces this noise over the ground plane. I couldn’t believe I didn’t figure this out earlier! Finally I may begin enjoying my Fostex PM 0.5’s again. Sweet.