iPhone 5 annoying rattle sound when shaking!

Hey guys,

I have recently bought my iPhone 5, and then suddenly I noticed that when shaking it is making a little rattle, its kind of something is loose inside it. I've hold down the sleep, silent, + and - buttons while shaking and still making this rattle sound. I'm certain its something inside it, like the accelerometer, compass, or any other, and it has never fell down to the ground.

Once this iphone is still under Apple's Limited Warranty, i must exchange it with a new one, or apple wouldn't accept to exchange an iphone just for a noise?

thanks !