Waterfreak is correct this is a normal noise (rattling inside of the transmission at shutdown), just shut the car off with the clutch pedal depressed. As far as the rough idle it's just one more thing you'll have to get used to driving around in a 405 HP car, well that and all of the staring and waving
I hope you are enjoying your new car. I"ve had mine for 4 months and love it more every day.
