I just got two of my basses back from having setups done and Audere classic preamps installed. They both made these horrible popping sounds when I played hard, and I could see the speaker moving on my amp like it was getting DC voltage. After a little experimenting I saw that it only happened when the strings hit the pickup pole pieces (or maybe just got very close without touching - not sure about that yet). Obviously I can lower the pickups, and I will. But is that normal behavior, or do I have some kind of grounding problem?