Forward of the jack mount, there is a small metal flap that is removable for access to electronics and wiring. On the passenger side there is a black controller box for rear lights, towing, … I think. That was rattling in mine new upon purchase.
My passenger van jack isnt mounted like or look exactly like yours....dang it. The rear barn doors if I grab them firmly seem to rattle, maybe at the little latch down below, maybe its that? going to try putting foam on the latch.