My Fender P-Bass's action has to be set really high to keep the upper registers from buzzing. The bridge is high. Lowering it brings buzz to the frets. So I keep it high. Is it my bridge? Or is it my truss rod? The opening is located near the nut, but I don't know what to use from there. (allen wrench, screwdriver?) Its a 2003 Mexican Fender Standard. What do I do? I'm starting to hate playing the thing.