My C string is buzzing at the 12th fret. This is extremely annoying because its the only buzzing spot on the fretboard, and i can't seem to isolate the fret its buzzing against. I've tried raising the action and I have to raise it to very uncomfortable levels for the buzzing to stop, so i think the fret its buzzing against is closer to the nut. I've heard you can sand down the fret or do a truss rod adjustment. Help please!