Mine was doing the same thing. I seldom use that seat so I flipped it up and it stopped the squeaking.

When I have a kids car seat back there I noticed the squeaking stopped. So know I keep a big Rubbermaid tub with my recovery gear stored on top of that seat and no more squeaks. But if I'm riding around with the seat down and no weight on it, it squeaks.

The most reoccuring squeak by far would be the hood latch. I have to spray that quite often while on the trail.

'97 T100 SR5 XCab 4WD
TRD SC ~ ARB ~ FWC
'85 FJ60 Landcruiser
4E9 ~ locked ~ 33's