I guess I've been lucky so far with my SRT-6 (knocking on wood now) that I haven't heard this rattle yet after 6,500 miles.

I do know exactly what rattle you guys are talking about though...
my wife had a regular Crossfire for a company car a while back and it had the rattle from day one with less then 100 miles on the car.
I never did figure out what it was, before she had to turn it in for a different car.

So...all this time I've been thinking and hoping it was just something to do with the active spoiler rattling in or on the hatch, since my SRT-6 hasn't had the problem yet after 6,500 miles, but I guess not.