Just got my 5s gold...the lock/power button rattle was so loud it made me jump this morning when I put it in my pocket as I thought the phone was turning on.
So I got to thinking...I just got my Spigen Tough Armor Case...I was eating and Organic Apple and before I bit into the apple, I removed the Organic sticker that they put on the skin...
Did some more thinking and removed the Case on my 5S (as it did not remove the rattle, took the edible apple sticker and folded it over onto itself lengthwise so that the sticky side was out, placed it over the lock button, put the case back on and Viola...no rattle.
Just saying, sometimes an elegant solution is right there in your refrigerator...peace.