When I bought my 4S it had a rattling noise and it got me worried, that was about 2 years back, and it still is doing a splendid job. No problems at all, it is just a mechanical noise that is perfectly normal, as there are moving parts in the phone. I now have a 5s, and it has exactly the same noises, I have no intention to swap a perfectly working phone. A plastic phone would probably be quieter, but I like the metal and glass construction.