2019 Toyota Tacoma 4x4 Unknown rattling

Wondering if anybody has had experience with a mystery rattle behind the front seat, possibly in the storage area or under the bed of the truck.
I removed everything from under the storage compartments under and behind the seats I still have the mystery rattle. I also removed the towing ball nd fixture to no avail.

 

Seat belt buckle from the rear shoulder harness against the plastic maybe?

 

I'm checking that out today thanks, I won't rule out anything considering it's driving me crazy to have a rattle on a truck with only 6k miles on it. However, it does sound more like sheet metal rattle. I may have found the issue though. yesterday I crawled under the truck to look around for anything loose and found the right rear shock is covered in an oily substance like hyd fluid/oil, I'm thinking that shock blew out. I have an appointment with the dealer this morning

 

That's no good! Hopefully that's the cause. Good thing you crawled under and found that!