Have you noticed that your iPhone rattles when you tap the camera area on the back? Turns out that this is completely normal and is a result of the gyroscope inside your phone. It is definitely very annoying, but at least we know that it is not a hardware issue with your phone. You can test out the noise to make sure it is not that loud by tapping very lightly on the back of your iPhone and listening to the rattle near the camera. Of course, if it sounds like something is truly messed up (if the rattle noise is unusually loud) then you should take it the Apple Store and have a genius look at it.
Hope that alleviates any concerns you were having over your iPhone. Let us know in the comments if you know of any other weird issues on your phones.