I agree with you and others that have said it does not affect how I use my iPhone. But for quality control sakes .it really should not rattle at all. Just saying .. Unless there is an app out there that uses the shake effect to use the app there is no need to shake a phone. But you can say the same thing about any product. If i shake my MBA ..i would expect it NOT to rattle.
Are you sure it shouldn't rattle ?
We don't know what is the rattling part.
We don't know if it isn't something related to the power button which is there to improve it reliability (Apple had some issue in the past regarding power buttons ) ....
If you shake a blue ray player, for instance, maybe it will rattle. Is it defective ?
As far as it didn't affect my real life usage, FOR ME this is not an issue.