I've had my 64Gig White AT&T iPhone 5 for 13 days. I noticed the rattling sound right off the bat. It's not the thud of the battery being loose like some people are also experiencing.
It's as if a screw is loose inside. And when I tap by the camera it makes a rattling noise. While I think that is normal as most of the phones that I have tapped do this. I agree with others who have stated that you should hear a rattle when you tap by the camera, but no sound when you shake the phone.
Well, mine has a fairly annoying rattle when I shake the phone. So much so that I can often hear it when I put the phone down, or when I quickly pick it up to hold it in my ear to make a call.
I went to the Apple store today to decide if I am going to return it and I shook and tapped every iPhone 5 they have as well as most of the iPhone 4's. Every one of them made a noise when you tapped by the camera, but most did not make a rattling noise when you shook them.
So, yeah, going back. They can either replace the phone if there are any stock if not, I want my money back and I'll just wait a bit until their QC has improved. I might even wait and get on the S cycle or get a different handset altogether. We paid a premium for these phones. We should get what we're paying for.