I just bought a K&K Bass Max pickup and I am getting a really terrible papery sound from it. The sound between the E/A and D/G is also really uneven. I am not sure if this is due to my strings or the way I installed it. I have a Shen SB-90 with Eurosonic White (Presto Nylonwound) strings. The bridge slot was very tiny, so I had to file it down. I filed a bit too much, but the Bass Max still stays in place when I put it in, it just doesn't pick up very well. I inserted a small piece of cardboard as recommended in the instructions, and this helps with the volume, but the pickup still sounds bad, especially at higher volumes. I am getting a really loud papery sound when I hit the strings and this is present without the cardboard shim, but more so with it. I have tried re-positioning it over and over and I've also tried it with and without a preamp, but nothing has worked. I really don't want to refile the other side and try again only for it to not be any better. Is it possibly my strings that is making that sound? Even aside from the sound, the pickup still sounds really uneven and unclear. Can the cardboard be causing this?