[INFO] Found the source for the rear door rattle

Not sure if you hear it with stock setup. But in certain songs there will be parts that resonate with something in the rear doors. Good song to test with is Erreur 404 by L'Impératrice. IF YOU HAVEN'T HEARD THE RATTLING DO NOT GO LOOKING FOR IT BECAUSE YOU'LL NEVER STOP HEARING IT.

That something is the mechanical latch cables. There's a few of them but the worst offender is the cable that runs vertically from the outer door handle. The solution is really easy, lash it to the horizontal running cables. I used soft velcro cable tie downs. Circled in red.

I also zip tied the horizontal cables to the frame of the door near the center pink screw point.

Without putting my sound dampened door trim back on this has eliminated pretty much all rattle coming from the rear. Only other door I need to investigate now is passenger front. Likely a similar issue.

 

See those two cables running horizontal coming out of the vapor barrier? There's some cables just like them running vertical just behind the metal panel (gotta peel back the vapor barrier there to get in).

Those vertical running cables to the door's OUTSIDE mechanical button will resonate at certain frequencies and rattle awful. I noticed if I cut rear door frequencies at about 400-500hz and below it would mostly remove the rattle. But I didn't like sacrificing fidelity so I ended up fastening the vertical cables to the horizontal cables. It's not a perfect fix but it's about 98% resolved and that's probably going to be imperceptible when I get the trim back on tomorrow.