The ESP Guitar Company

Okay, NGD. It is super awesome, but something is bugging me. On the A string, if I pick it open, picking upwards instead of down, there is some buzz. If I downpick it sounds fine. The string is definitely NOT hitting the first fret. I'm positive of that. Also, if I lightly touch the string behind the nut (even with no pressure), the buzzing disappears. I've loosened the string to see how the nut looks cut, and it appears pretty normal to me; nothing crooked, out of wack, and no chunks missing. It isn't cut loose either. The string appears to sit in the nut just fine. Any ideas on what this could be and how to fix it before I try the "new set of strings" route?