I've got a strange specific problem. For some reason unknown to me, my seagull s6 buzzes terribly on the g-string at the seventh fret. it's fine on every other fret, and every other string is fine on the seventh fret. what is causing this and what should i do to fix it? i've only had the guitar for about a month and a half and haven't changed the strings, i'm not sure what kind came on it. thanks in advance.