Wife just took car in to VW and the ticking noise stopped as she drove up. They have no idea what it is. Amazing, a forum on the net has all the details and the mechanics have 'never heard of such a problem'. The old forum has plenty on this topic and it does seem as though this is a natural thing to happen, in fact the ticking noise means the solenoid feedind diesel to the rear heater is working!!! Would have thought they would have tried to damp the noise a bit though. I'm going to book it in, under warranty, and demand that the noise be dampened. This is a great site, really put my mind at ease when I read similar problems/issues coming up.