Nut problem - Too big or too small?

[JoeRules00]

I've got an issue with my SX Jazz, an open 'A' causes a little buzz in the nut/lower headstock area. At first I thought the string wasn't settled well in the nut, and I would need to file it a bit, but the idea just came to me that the nut may be filed too much, and the buzz comes from the string rattling in the nut. Is there a clear answer to this? From there, I'll need a little help too, but I want to diagnose the problem exactly before I took any action.

Thanks!

[HeavyDuty]

Detune the A a bit and see if it wiggles in the nut. Also, you can try laying a small piece of paper in the A string nut and retuning - the paper will act as a shim. If that's what it is, either cut a new nut or try the super glue and baking soda trick (search for it here).