ok, well I fixed the issue on my end finally.

After tearing apart the rear trim of my car three separate times and laying down a few pounds of dynamat xtreme, adhesive felt, and foam weatherstripping I finally took a less "carpet-bombing" approach and isolated the issue.

The best way to do this was to take out the back seat back, side trim pieces, and parcel shelf and rear plastic trim pieces that sit directly behind the seat back. Or if you are lucky and it turns out your issue is identical to mine just remove the aforementioned plastic trim and side trim BLACK ONLY from the passenger side of the vehicle, put the bottom of the seat back in, and have someone drive you around.



That red circle was the source of my annoying tap tap tap rattle sound. The sound itself I could have sworn was a loose wire or plastic panels tapping each-other. Instead it was being caused by two pieces of stamp pressed metal that must have had just a few microns of travel between them, the sound would carry up the rest of the sheet metal and appear to come from the parcel shelf itself.

My solution was to remove the small clip holding the trunk liner to the metal, gently pry the leading edge of the metal outward, and then cram that gap full of dynamat (cloth or anything to reduce noise should work just as well, crimp the metal back into position and NO MORE FRICKEN TAP NOISE. My life is so much saner now, I hope this helps!