I had an Aguilar OBP-3 installed to go with my EMG-J set. I'm running the system at 9 volts. It sounds awesome but when I sweep the volume pot, at some point during this motion the bass makes a 'scratching' sound as though the pots are dirty. The pots have been cleaned and changed but still the same problem. At the same time I can see my speakers move briefly as though they're receiving a voltage spike. The preamp was returned to Aguilar and they said that there is nothing wrong with it. The pickups worked fine before I installed the preamp. I'd like to know if anybody has had luck with this combination; or just let me know what we're doing wrong.