It sounds to me like mild classic dieseling. Are you familiar with dieseling? It's when the engine runs on after the key is turned off, usually the engine shakes like you describe. the rattling noise comes from preignition just like spark knock and sounds like a diesel hence the title. Check out this for the description and possible cures.

http://en.wikipedia.org/wiki/Dieseling

There's a valve on most cars that turns off the fuel supply immediately when you turn the key off so the car won't run on, if it's defective and the engine has hot deposits within the cylinders, or the spark plugs have deposits, they will ignite the fuel even if the key is off. Good Luck. Keep us posted.