G string, 12th fret...sounds weird

The intonation might be out which would make it sound out of tune. i'm not sure where that low end sound would come from.

To check the intonation get a good tuner and check the G string fretted at the 12th fret and the natural harmonic at the 12th fret if they are both perfectly in tune you have no intonation problem, however, if the harmonic is sharp or flat turn the intonation screw on the G string saddle, it's the long one that comes from the back of the bridge to the saddle and has a spring around it, turn it a bit at a time until both note and harmonic are identical. Intonation is the variation in a strings tuning as you fret closer to the bridge end, the string stretches more the shorter it gets and goes slightly out of tune, intonation adjustment helps but isn't perfect, however, the longer the scale the less of a problem, one reason Gibsons early basses, which had 30" scale length, were avoided by most players, opting instead for Fenders and Rickenbackers

Dead spots