The rattle I found was caused by the vibrate switch being loose when vibrate was off. The switch is tight and the phone doesn't rattle when I shake it when vibrate is on. When vibrate is off, there is a tiny bit of free play and this causes a rattle. I didn't want this to turn into an issue later on so I made a concierge appointment. The genius heard the rattle and offered to swap the phone. The new one is tight so it is a defect. All is good now.