I am a fairly new bass player. I recently purchased a Gallien-Krueger MB210-II Combo Amp. I find that after playing awhile, the amp's fan starts making a muted, although noticeable, high pitched noise. Is it normal for bass amp fans to make this type of noise, or have I received a defective amp? I've only had the amp for a week, so I can still return it. If I do end up returning it, is their another bass combo amp in the $700 range that I should consider? Your comments would be very helpful.