Quick favour to ask...can anyone fold their passenger-side REAR seat (the single one) down, and take a picture underneath the seat cushion (bottom) part, of where the seat connects into the floor of the truck?

On mine, there is a large bolt covered by a plastic cover in the middle, then 2 guide-style screw ends sticking up on either side with a rubber stopper. Looks to me like bolts may be missing, but not sure. Maybe previous owner removed and didn't put back.

Trying to isolate a loud noise over bumps and it seems to be better when the seats are down...trying to see if something's loose (a bolt, maybe the seat backs, or the latches on either side that connect to the body sides?

Any help appreciated!

 

Interesting. My '07 is the same way. I have the single center bolt with plastic cover, then body-colored small bolts sticking up through oval holes, with no nuts.

 

I removed my seats many years ago.. There are 10 nuts that hold the seats & backs in, some have rubber protectors on them(shown in picture).
Here's a pic, (pardon the construction debris):

 

That is correct. 1 nut on the seat and 2 guides to prevent the seat from shifting, keeping it straight. Drivers side rear seat has 2 nuts, therefore don't require the guides.