When I have my tone knob turned toward the treble side, I have an unbearable hum that will not go away. The hum decreases as I turn the knob toward the bass side and completely disappears with the knob on full bass. When I first received the bass, I had a bad bridge ground that caused the bass to hum all the time. I fixed this by sanding the bottom of the bridge to the base metal and adding a little copper stamp of shielding copper between the wire and bridge. Now it's dead silent on the bass end but hums on the treble end of the tone knob. What do you guys think the issue is?