Here's what Iv'e been told by someone who should know, the lucky bastard gets to do the reliability testing after all.
The issue is caused by a resonant "shake" that is different to sedans and the noise is from the gear teeth on the back adjuster. That is, the seat is flopping back and forward on the gear teeth, put a pasenger in or some other load on the seat back and it goes away. The usual "fix" is to simply lay the seatback back a bit further to put some preload on the gear teeth.
Hope that solves the puzzle.