It is the camera...as someone else mentioned I can confirm when you tap the top part of the screen, you get a quick rattle, only really noticeable in a really quiet setting. The harder you tap the more noticeable/louder it is (which is the reason for my question below).
Turn the camera on and tap the same section of screen, no rattle.
It shouldn't, but little things like that bug me. Even though I know what it is for sure; it still bugs me.
I wonder though, since that rattle is indeed the camera MOVING in the phone...can you then rattle it enough, tap the screen hard enough, enough times, to actually mess the camera up?
Seems reasonable to me that anything contained in something that's lose enough to bump the edges of its container could be damaged this way? Maybe not though?
Just drives me nuts because I hear it all the time often leaning my phone forward to meet my thumb to tap the top portion of the screen (essentially tapping the phone to my thumb rather than straining my thumb to reach the top of the screen) especially when browsing web sites.