Hey, for christmas i got a used Centaur (old company) powered mixer- It has 6 channels and 165 watts. I recently had it on for longer than i have before, maybe an hour- and without touching it it started to make "clipping" or "pop" noises. (i unplugged all the inpunts and it sttill made the noise. any ideas on what it could be or what i could do to fix it?