The rattle is the inside skin of the exhaust tips, they go loose over time thus producing the rattle, once warmed up it goes away as it expands with heat.
As to the noise, I don't have that on mine...
oh so its not in the baffles of the actual box then? it does go away when warm as you say, but its not a good image to have a rattling exhaust, makes it look like you're driving a bag of bolts! i was considering changing the rear for a scorpion set up with non resonating centre pipe, the current setting is just too loud