Little Hawk, did you make sure there's not a thumbpick hooked on the high E string, down near the bridge? That'll make a guitar buzz.

The last time my guitar buzzed, it was the downstream end of a string, resting on the spruce top. I had let too much of it stick out of the knot. I clipped it off, and that solved the problem.

On my dulcimer I can get a buzz when the butterfly stickers which mark the minor chords curl upward and touch a string. Do you have any stickers on your Martin?