A couple of weeks ago there was a post about a B string that was buzzing when fretted at several locations on the fretboard. I theorized (boldly) that perhaps a pinch at the nut was causing the problem by creating two points of contact, but promised to try to contact Trevor Gore (who, unlike me, would actually know what he was talking about) to see what he thought. Turns out, my speculation seems to have been correct. According to Trevor, a pinch at the nut can create two points of contact and produce two active string lengths that can closely match up and create a resonance (which is basically how a sitar works). He mostly shot down my other theory that a pinch could possibly create another resonant frequency in the top. He said this conceivably might only occur if the T(1,1)3 is very close to the T(1,1)2 and both close to a scale tone frequency.