i recently got a refurbished iPhone as a replacement, and now every once and awhile when i get a text message, it wont ring or vibrate, which is annoying. and then some other times, it will not make a ring, but vibrate, and then the screen flashes a couple times, turns off, and then i get the message. its annoying, should i go in for a replacement again? would they even give me one or so anything since there isn't anything wrong with it most of the time? and quick fix it ideas?