Whenever I fret a low F on 4th string, it comes out severely sharp, to the point of almost resonating as a minor 3rd with the open A – a half step difference! The 12th fret harmonic is in tune with the open E so I've ruled out intonation as the culprit, plus the problem doesn't extend to any of the higher frets (if the intonation were off, the problem would only get worse going up the neck, right?). So logically, I'm guessing the issue has something to do with the height of the 1st fret... would a fret level be in order? In my two years of playing, I've been lucky to have had no issues beyond anything a DIY saddle/truss rod adjustment didn't fix, so I'm sort of at a loss here. Thanks TB'ers.