I just bought a new Gallien-Krueger MB150 combo and I'm wondering if what I'm experiencing with the amp is normal. When I switch it on and, after a few seconds, the power/protect light goes from red to blue there is an audible hiss which remains for as long as I have the amp on. When I switch the amp off there is a little "pop" sound which comes through the speaker. This hiss stands out to me because none of my other amps produce any significant hiss (I should mention that the hiss with the GK is consistent and is not affected by my turning up the volume or output knobs). The other thing is that when I engage the limiter the hiss essentially doubles in volume. This doesn't seem right to me but I've never used one of these amps before so I don't know. Any thoughts?