The turbo warranty has been extended to 82,000 miles/8 years so if your car is under that then you have a lot of backing on your side. I suggest taking it to another dealer and complain to them about the WG rattle and see what they do. If no luck there then get in touch with BMWNA.
"I'm not surprised you get along well with all the other neighbours. If you put fifty children with Down's syndrome in a room there is going to be a lot of hugging." David Thorne