Hopefully I will know more when VW Customer Care get back to me, hopefully tomorrow - they have promised an explanation as well as reimbursing the labour cost I had to pay.
I am guessing that the discs were most likely corroded, the car did sit around for a few weeks before delivery on 1st March. It was supposedly tucked away somewhere out of harms way during that time, but I'm starting to wonder if in fact it was sat on the dockside somewhere in the salt-laden air. nothing else seems rusty though............
Kenny C - if it helps, this noise was both variable in volume & intermittent, sometimes rattling like crazy very frequently, other times just a faint tinkle once every few days.