Sirion clicking noise in boot


We have a 6 month old new-style Sirion and (mostly) love it.

It has however one fault that is driving my wife crazy. After driving for a bit there is a clicking noise that appears to be coming from behind the rear pillar moulding on the driver's side. Initially we though it was the seat belt (maybe the inertia reel), but now not so sure. It doesn't start immediately, and it doesn't seem related to speed or road surface. Is there anything solenoid operated in that area that could cause the noise (fuel solenoid?).

We'd take it to the dealer to fix, but since its not always there is a bugger to get anyone to take seriously.