My new amp arrived about three days ago and I've only just noticed that it's humming a little. It isn't audible when I play, but it is kinda audible when I don't play anything, and even hums a little when I turn the volume all the way down. The amp in question is a Hartke HD50, brand new. I made sure it wasn't the bass by plugging it into my previous amp, a 10 watt, and turning the volume to the same level that I was playing at with the new amp and the old one wasn't humming, or atleast not to same degree(if you listen carefully, you can hear a very, very slight hum). Is there something wrong with the Hartke or is the hum normal?