Hey guys, sorry if this has been asked before but... I just got my hands on the 5150III LBX. I plugged it in for the first time, and with the volume set to 0 I get my guitar coming through. It's not loud mind you, but odd. It's also accompanied by a low hum that is only affected by the resonance control. Turning up the volume doesn't make this hum any louder and this is with nothing plugged in. Anyone else experienced this?