noise when shaking, noise when shaking

I just got my Iphone 5 3 daysago and i realized that I hear a noise everytime I shake the phone even when it is a very gentle shake. It seems like its coming from the buttons on the device because when I hold the buttons and shake it i hear less noise. I wonder if this is normal, I was using a 4S before and that device doesn't have the same poblem. And just for the record I have never dropped it no it was demaged in any other way. And the buttons and everything else is working just fine.