my original question was probably phrased in a stupid way: I realize that it isn't normal for the wheel to hit the stay, so I guess I'm wondering if

a) it is a common problem with Al frames and a sign that the frame is wearing out
b) can be attributed to a crack somewhere that I need to look for (not quite sure how/where they appear)
c) it could be a problem with the wheel other than dish--like can the wheel flex if the spokes are not tensioned properly.