On Mon, Nov 16, 2009 at 11:41 AM, Luther, Ron <Ron.Luther at hp.com> wrote: > My best guess is the infamous ground line hum: > http://en.wikipedia.org/wiki/Mains_hum yup. it's that 60 Hz hum. I'll play with electrical connections and see if it's really the amp, or just my dirty power. (you didn't know I had dirty power, did you?)