The camera rattles in a lot of models, and so does the home button. This is just the way it is with the iphone. Every year we go through this, both problems vary from phone to phone, and some are louder then others, as well as some not exhibiting either problem, however those perfect ones may have a dead pixel or two, or be scratched out of the box....Lol, it's just the way it is with these phones these days. Apples quality control stinks and is just not what it was years ago.
Unless you have the patience and the hook up more importantly either in a corporate store or Apple to go through a bunch of iphones your going with the luck of the draw. With my 5 I went through about 7/8 brand new white iphones out of the box and every single one had an issue, whether it was a very loose power button, scratches on or around the chamfered edges, etc etc, perfection just wasn't there. So it comes down to are you ok with spending hard earned money on something that isn't perfect? Is what it is...