Pictures don't lie, right? When we first tied the two sections of the right wall together, I noticed that there was very little clearance in a few spots. I figured there wasn't anything to do about it until everything was locked in, so I'd worry about it then. Well, it's then - and here's the photos.
First, with a strong back light, we see the right wall. It's clear that the concrete wall is not smooth. It's plumb, overall, but wavy.
Second, to my surprise, the studs are also plumb. I checked several of them, and the picture might be a little difficult to judge, because of the angle, but the bubble is between the lines. The level is about 4 feet long and does rock a little on the surface of the stud, but the bubble doesn't break passed the line no matter what - so I'll call it plumb.
The left wall is the same story, only if you shake the walls, the rattling is always from the right wall.
So, what can I do? Should I ignore it, and hope the wall doesn't move and bump the concrete? Should I leave a shim in there to firm up the connection and keep it from rattling? Should I carve out a little of the edge of the stud - tracing the profile of the concrete? Are there other options?