As if my two cents matter.
First, most people who are complaining are not tapping looking for a rattle. This noise happens when you pick up the phone, place it on a table, and when makiing a call even when a touch to the upper camera corner is made, and is pronounced enough that the "camera lense" excuse is not holding water.
I came to this belief after having two iPhones 5's (first one was scuffed and chipped, so it was returned) and shaking and tapping all the display models in the Masonville Mall (I went to complain about the rattle, but then realized I was like everyone else, going to have to live with this issue). All of them make a noise when shaken (camera focus component, also found in the 3GS and 4/4S) but ALSO what sounds like a component "clicking" against the glass. This too may be the camera, but to me, it sounds like something is loose or not installed correctly, or possibly a design or production flaw.
The proof, in my opinion, that this is not simply the camera lense, can be experienced by simply adding a slight amount of pressure with your finger to the camera and then tapping the back of the phone. The sound will be significantly muffled. Thus, it is a noise from the GLASS! Not simply the internal part of the camera.
Furthermore, if this sound were made by the "vibration motor" one would expect it to only worsen when the vibrate function occurs. But of course, it does not.
Anyway, this is not my first rodeo, and not my first iPhone. In fact, I have had two 2G's, one 3GS, an iPhone 4 and now two 5's in my house, and NONE of them have mode this sound. Yes, the camera has a slight noise in each when you shake the phone, but the rattle I mean, and which I believe most people are talking about is, something else altogether. AND FRANKLY, IT IS IRRITATING, especially on a phone that costs an arm and a leg.