So, on investigating the emergence of some new rattles from the general upper "b-pillar" area
, I've discovered that, on both sides, the internal upper cover piece (this is the biege/light grey piece, that surrounds the seatbelt anchorage at high level) are really seriously distorted. 
Looking at the car from the outside, when you look at the leading (i.e. the almost vertical) edge of the rear side window, you can see this piece of cover piece emerging from behind the "printed" edge of the laminated glass -- it's not constant distortion, the rear edge of the plastic piece that should be hidden behind the "printed" edge of the window waves about all over the place. If you push on this plastic, you find that it's broken off its fixings (if it has any) and just wobbles about. On the driver's side, it's so bad that looking at the car from the outside, you can see the "inside" of the cover piece and can see the stiffenling ribs on its inner edge (which obviously don't do their job).
Now that I've seen it, I'll just keep seeing it. Grrr.
Still, another reason for it to go back. I was going to get the dash rattles tackled again soon, anyway.
I just thought I'd point this out to you guys -- somethng (else!) to keep an eye out for. Trouble is, aside from Mole, I've got one of the oldest 9n's on this board, so I think this is a problem that will emerge in time - as the plastic "relaxes" from its original shape. Not good.
Deek
(This is all on a 3-door, btw).