Should i trade in my iphone again?

SO i got an iphone 5 about two weeks abo and then went on vacation, while on vacation i noticed that i could hear something very loose in the iphone, my brothers iphone 5 had the same sound you just had to shake the phone much harder to hear it. When i returned home i went to the apple store and with a little persuading the apple genius took it back because i was still in my 14 day return policy, i got a new iphone 5 and i have been using it for about a week and now i have noticed that not when you shake it but when you even lightly put it on a surface or tap on it you can hear a rattling like in the last one. Once again on my brother's iphone 5 you have to tap a little harder to hear it and you have to basiclly drop the phone to hear it when putting it on a surface. My question is, do you think i should take this one back and try and get it exchanged or is it something that all iphone 5s have, also do you think apple would even take it, or would they not consider it a problem? Also i was wondering if anyone has an iphone 5 on ios 6.1.3, how long does the battery life last, and have you ever made it through more then a day without having to charge it with regular usage?