Hi Kenton, welcome to the Audi-forums.
Its a bit difficult to describe a rattle I know & there can be so many different types that it is hard to say without actually hearing. I have a slightly audible rapid clicking sound when I start up which gradually fades and is inaudible from inside the vehicle. To be honest I dont know what causes it and seems to be normal but is perhaps the same thing. It has never bothered me overtly. Lets see if there is anyone else on the forum that can throw some light on this.