I just received a new Gallien Krueger MB150E microbass combo. I noticed as soon as I plugged it in a "hissing" sound, it almost sounds like a it's a white noise generator. It's not a hum, which I'm familar with from my strat playing days, but an ambient hiss that I would put on if the neighbors were fighting and I wanted to sleep. When I play I don't really notice it but when I stop playing it is noticeable. It's especially noticeable when I plugged headphones in to do some quiet praticing, the noise was unbearable through the headphones. I've plugged guitar and bass amps into the outlet I'm using and no noise, so I don't believe it's bad power. I actually just had a guitar tube amp plugged into the same outlet yesterday and didn't notice any "hissing" sound. I've tried two different outlets and no difference. I've played with the controls and even set the controls to "walking bass" setting per the manual and no results. I really like the amp, it's loud and light. But the noise issue is disappointing. Is this a known issue with the microbass amps? Any suggestions on how to fix this problem? Thanks.