I have a peavey nitrobass connected to a peavey 4x10 4 ohm cabinet. Occassionally the lower speakers will "thump" or "pop" 6-10 times or so then stop. I've tried turning the volume and gain all the way down when this happens to see if this was the culprit,but no difference.I've also turned down the HF control on the cabinet,but again,no difference. My gear is about 6 months old and hasn't been abused. I've also tried all three ground settings. I'm wondering if this might be a power issue?