Most iPhone 5s users are annoyed by the rattling sound made by the Home and Power buttons. Some even found that the battery was loose and caused a sound when the phone was used or shaken. The problem is that when users went to the store for a replacement, they realized that all new devices have the same problem which meant that nothing much could be done about it. You can get a loose battery fixed, but you will just have to find a way to get used to the noisy buttons since replacements will have the same problem.
iPhone Guide iPhone 5S Rattling Buttons