My 2007 3.0si had the 3rd row seating option, which in hindsight, I know now is total rubbish. More problems than good...so happy my 2008 4.8i does not have that "option".

When you unlatch the back seat, and push it forward (it does move forward & up quite a bit), there are latches and grooves on the car floor. I found that greasing them with white lithium grease, or silicone spray eliminated almost every "rear seat, back of car" rattle. Hope this helps!