Four days ago I have purchased a B7k. I've tried it briefly the same day at my band reharsal, and then today is the first tme I've had time to sat and try it well. I've noticed a high pitched noise, and it becomes louder increasing the level knob. Include a clip recorded with my phone. The effect is really loud because I've raised "level" to almost max just to be sure I can record the sound. Anyway, toward 10 seconds seems like i'm loading a game on an old Spectrum... Never had this prolem before. Should I be worried?