Car is fixed by replacing the donut gasket! AMS will be supplying the gaskets with every purchase of Downpipes. Case Closed! Everyone should make sure that they properly install everything and make sure the gaskets aren't damaged or compromised in any way especially if you take your exhaust off and on a lot... Thanks to everyone for sharing and thank you AMS for the resolution.
Here is the link to the gaskets
http://www.realoem.com/bmw/showparts...52&hg=18&fg=10
On that drawing number 7 is the gasket you need to replace and the rattle is caused by number 6 flopping around.