I see have not explained this well. The note buzzes when the string is completely open. The chord bars are not skewed, bowed, or pressing on the string. It just buzzes when you play it and it can vibrate freely.
It's *very* annoying.
I can't see anything wrong with the pins or the string's winding (though one of the top strings on this harp seems to be unable to stay wound around its peg -- the cut end keeps slipping through the peg's hole and popping out. But this I assume is fixable either with a slightly longer piece of the same weight wire or something). The string just buzzes for no apparent reason.
Perhaps it was sired by a sitar.