Re: Single note fret buzz
may be the 6 th fret. Take something with a short straight edge, maybe like a ruler or stout business card and set it on the 6th fret and see if you can rock the card or whatever straight edge. If it touches all three frets, they are fine, if the card rocks then you have a high fret. could be as simple as lightly tapping on the fret to reseat it, but you probably wont know for sure until you tell if the 6th fret is in fact too high.
Have you changed strings recently ? did the problem just start to happen with this set or has the problem continued through multiple string changes?