I have a similar experience. Rattle sound coming from the roof, when I looked around it looks like my roof rail delete, just the flat pieces that covers where the roof rack would be, was loose. Next time its in for service I will have them fix it because I don't know how it should be secured, but the rattle was from the very front driver side not being secure at all. It would wag like a dogs tail left and right at the speeds you are having your issue.