Whenever I play my A String, there is a strange buzzing/vibrating sound that comes from near the headstock. I'm positive it's not fret buzz, and if I apply pressure to the string between the tuner and the nut, the noise goes away. I believe it may be something up with the nut, since I just had it replaced at a local shop and it had never made the noise until after the repair when I replaced the strings. I was wondering if anyone had ever come across this and could offer any advice as to what it may be. Any help from you guys would be much appreciated 