Read a lot of the posts here but Mine is a bit different. It came from the drivers seat (rear right side bolt.) At first I thought it was the bolt so I put down some foam. Turns out its actually the floorboard. I'm not exactly sure how Nissan built this but it appears the threads are part of another panel that sits under the floorboard and however its attached its whats creaking. It actually gets quieter the more I back out the bolt, tighter actually makes it creak more. When you tighten it all the way down and rock the seat side to side you can actually feel movement from under where the bolt threads into the floorboard. I tried all sorts of lubricants but so far none work. what a pain....