In my 2.8 (non M) I don't have leaks unless it's really raining, HARD, so take it in and make sure they fix it under warranty, you shouldn't have to deal with that. You paid many thousands of dollars for the car, make it worth it! As far as the rattle, if it's from the rear (not the seat, but the rear tire/suspension area), it could be the parking brake cable. Tighten it up from under the brake handle boot, email if you want more detail.