I went for a test drive this past weekend and found myself in a bit of traffic before getting to the highway. I noticed that the car would make this rattling sound when lifting my foot off the gas in really slow moving, stop and go traffic in 1st and 2nd gear..... almost like a knocking sound from the rear. The owner said that that's just the way it is and that the car isn't built for traffic like this.... kinda made sense at the time. Is this common for early NSXs? Or is this a problem that should eliminate it as a purchase candidate? It drove like a dream on the highway and there was no sign of the noise over, say 10 mph. If I were to take a guess, I would say its the stock exhaust shaking but I looked at the exhaust afterwards and it seemed to be attached solidly. Any thoughts?