I've been attempting to track down the worst ****ing rattle in my '12 sedan... I've performed this tutorial twice already, I've stuffed more dense foam up under the rear deck lid as can be stuffed under a rear deck lid, and am still plagued by this creaking. It sounds like a tinny, higher pitched creak, not so much a vibration. Every little bump, side-ways motion, even louder than normal farts set the creaking off, and i can't take it anymore.
So I hired my roomate to ride in the rear to narrow down the cause, and I believe I've found the answer: the rear seat, namely the 2/3rd's side, is rubbing against the rear deck lid, causing the noise. I folded down the seats, and the sound isn't there. The smaller side in place, no sound. The bigger side: BAM! Annoying-as-**** creak returns.
Now that I know the cause, time to figure out a solution. Could take it to the dealer, but I'm not going to take off work for this bull**** until all options are exhausted.