The battery rattle is different than the vibrator rattle. The battery rattle is a loose battery that makes a thud when the iPhone is turned. It is documented with a fix in this YouTube video:
Noise Problem cured !!!
My iPhone 5 made a rattling noise when shaken after it had "a few falls"
I read in one of the forums that it was the battery coming away from the adhesive.
I checked iFixit teardown of the iPhone 5 and noted the very large battery which occupies two thirds of the screen space from left to right (starting from above the headphone jack side).
I'm not surprised that if it comes loose that it is the cause of the clunking rattle.
One of the forums contributors suggested gradually pressing all the area of the phone on the outside that overlies the battery inside pressing hard between front and back over all of the screen area from left to right that fronts the battery inside. In this way one pushes the battery back on to the adhesive !!
It works perfectly - Problem cured !! - J B Walsh
I've had my iPhone 5 for a month and today it started doing the battery thudding. I just gently squeezed the phone wrapped in a blanket, sort of like the video, and it worked perfectly. Not happy that this even happened, especially going back and forth between the iPhone and Galaxy S3 for months, but glad this worked so easily.