I'm on my 9th and final iPhone 5. Still has a very slight scratch on the back of the phone near the beveled edge, but I can live with it since it's very minor. I'm still annoyed that there is even a little scratch from a unit that I opened in the Apple store, right out of the box, but there isn't a RATTLE on this one, so I'm not taking any chances. The rattling is much more annoying than a minor scratch.
The only "NORMAL" rattle is if you tap the phone, right by the camera. If you shake it or put it down on a table or move it and it is rattling, that is NOT NORMAL.
I shook every iPhone 5 and iPhone 4 at three different Apple stores and 98% of the time, they did not RATTLE. Only when tapped on the back could you hear the rattle. I have friends with iPhone 5's and theirs never rattled, only when tapped in the back near the camera, you'd hear a slight rattle. Of course Apple retail customer service reps will tell you otherwise. They don't want to take the product back and if enough people are gullible enough to believe that this "RATTLE" is normal, the more product they sell and the more they can tell the next person that it's "expected product behavior."
If this were truly normal, then all those iPhone 5's and iPhone 4's at the Apple store that I shook to test, would have the opposite result. (i.e. most of them would rattle and only a few would not)