As I said in another post, I am starting to notice things about my new GT with all of 200 miles on the odometer. At idle, there is a really subtle clunking sound from the engine. I haven't noticed it before since I have had either the radio on or the AC on or both. But this evening I just turned everything off and rolled the windows down to enjoy the exhaust note. The odd sound goes away with rpm. Have any idea what causes this?