Common problem with the 03 and newer 4V heads that are under a lot of boost. The seats get overheated and will loosen from the heads. You can click on the first link to see the gap between the seat and the head, and the second link shows a video of the seat spinning in the bore when the valve job tooling hits it. 6 seats in this pair of heads were like this, all are being replaced.
4V exhaust seat falling out
http://www.youtube.com/watch?v=ObT2WAfhvM8