BluesHowler, since your guitar was originally setup at the store, I'm going to assume that you're happy with the action. If that assumption is incorrect, let me know.
The first thing I would check would be the neck relief. Begin by fretting the low E at the first and fifteenth fret, then check the distance between the bottom of the string and the top of the frets in the middle of the neck. Different people have different preferences, but I like to see no more distance than the thickness of a few pieces of paper. If there is to much distance, then you will need to adjust the truss rod. Begin by turning it 1/4 turn clockwise, then check the relief again. Continue until you're satisfied with the relief. Some people feel that it's best to wait 12-24 hours between each adjustment but I've never found that necessary.
If the neck relief looks fine, and the buzzing continues, then you'll need to check to see if the 10th fret is to high. Since it is only occurring on the A string, I would take a straight edge, like a ruler, and set it across the 10th fret next to the A string. If the ruler rocks back and forth on the 10th fret, then your 10th fret is to high. There could be a couple of causes for that.
First I would check to see if the fret wire has risen. Lay the guitar neck across your knees to support it, put a small block of wood on the 10th fret at the A string, and gently tap it with a hammer or rubber mallet. Then check with the straight edge to see if it is still high. If this reseats your fret wire, then the problem should be solved, though you'll probably have to repeat the procedure occasionally.
If that doesn't solve the problem, then you could try using an emery board to gently sand the 10th fret under the A string. Check it frequently with the straight edge until the 10th fret is the same height as all the other frets.
If any of this makes you uncomfortable, then you might want to take it back to the music store that did the setup and have them check it out. Hope this helps.
