Hi. I have an Epiphone ES339-Pro and I've just swapped out the pickups for some Gibson Burstbucker Pros (as a trial). Both pickups work fine individually but when I use them both together on the middle setting, I get a strange "dip" in volume on either volume pots as I reduce the volume from max. The dip comes in around 9 on the volume pot and then by around 8 it returns to normal. Like I said earlier, this happens on both pots turning them down individually. Any thoughts?