I thought it was them and it did seem when I turned off the lights it went away.....well that theory was short lived when the power supplies hummed again with the lights off....how romantic is that, lights off and the glow of two Astron power supplies....I digress.... I then ran an extension cord to another outlet that I knew was not on the same circuit as were the trouble was coming from. That seemed to be the fix things the supplies are running great now with no more hum. As I write this post it seems that the over head compact florescent light (that is on the same circuit) has a flicker to it. I changed the bulbs to incandescent lights and the flicker is still there. I checked the voltage at the outlet and it is 120.1 volts AC. I have gone down to the main panel and checked all the connections and they were fine. I am going to have to investigate loose connections and neutral troubles on this circuit this weekend. But for now the Astron supplies are running just fine on the other outlet.