I have a 2002 E55 with approx. 12,500 miles. During the last 300 miles or so, I have been getting a very unusual noise when I stop the car after driving it. It is not the usual light crackling you sometimes hear when parking the car after driving it. Rather, it is a fairly loud and high pitched pinging in the tailpipe area. It sounds like someone is tapping a metal spoon on the tailpipe every one or two seconds. It lasts for a minute or so after parking the car. It is highpitched and has a definite metallic sound, like metal tapping metal. Any ideas as to what it is? And should I be concerned? Should I take it to the dealer? Thanks very much! Also, it is fairly loud....I can hear the sound from 50 or more feet away from the car.