I just bought a Boogie 400 last week, and the thing plays like a dream. Before that, I only had a 50 watt Peavy MicroBass and a Crate BX 160. Needless to say, its a big step up. When I brought it home, though, I noticed a high-pitched whine that sounded almost like feedback, but I don't think it's feedback. When I turn the fan to low, the noise gets quieter, when I turn the fan off, the sound dissappears. The noise isn't loud enough that it cuts through, my signal from my bass, in fact, the only time I notice is when I'm playing at low volume, or when I'm not actually hitting notes. Does anyone know how to fix this?