Same problem here, Spent some time myself with some sticky foam strip this evening eliminating any noisy interactions and it definitely helped but there is still something underneath that rear plastic deck that is rattling.
All in all i'm about to go back and use up some more foam
Some soft targets I have tried:
Seat latch release brackets (The two you pull from the trunk)
A number of odd wires barely touching the lid (including the glowy green wire which had a metal clip loosely touching the frame)
Threw some foam to make a little buffer on the spare tool holder to cardboard bottom (Also tightened up the suicide jack so it wouldn't jangle)
Made sure spare tire holder was tight
Checked for broken clips/Loose/Rattly (Oddly whatever hose is on the left side behind the carpet was completely out of bracket)
Various places everywhere the carpet edge itself might seem to vibrate against the frame
Folded the seats down and stuffed foam under all of the wimpy plastic mini brackets on deck (Pretty sure there are more of these on the whole deck but I just got these) [Also noticed the frame layering quality was not very consistant...]
Foamed up various places around the trunk latch. (Oh god don't let it be the latch)
I can't say what helped significantly or specifically because I didn't do each one and then test, but it has definitely cut down on rattles, But still can't get loud without sounding ridiculous.