I had a bad rattle in that area on my 12. Took it to the dealer and they said that it was body flex/normal noise. After laughing at their faces I did some research. Tried the e-tape on the door striker/ tried to move the striker up down, left, right no use. The noise only happened around 60mph +.
After going crazy I found that a little clip had come off from the rear driver side fender flare and was rattling on a piece of plastic at the bottom of the flare. I was able to get the clip out of that area and the rattle stopped.
Morel of the long story, also check your fender flares.
If you want some pics locating this area just let me know.