Well you're in the right place 
Where's the rattle? Is it one of the common ones' that have cropped up on the forum?
Its in the engine bay, it sounds like its a fan that touches something while rotating, Its in and i got the technician to hear it so hopefully will be sorted quickly!!
It starts up sometimes when you sort of judder the car when pulling off, then it stays going, hard to explain really. But irritating non the less