It's a big bay - any ideas where?
What is the type of rattle?
Does it happen when you start up/shut down etc?
Dan 
Its at the center(ish) of the bay at the VW badge
It's like a ball bearing hitting off metal.....turbo?
It does it when I start up and leave it to Idle.
That sounds like either the PCV or the throttle valve. The turbo is at the rear of the engine, not far from the brake master cylinder resevoir.
A really obvious question though, have you actually checked your oil level, and when was it last changed?
