Ever since I got my car back from the dealer (transmission replaced and exhaust removed), when I remote start the car, there is a really loud rattle coming from under the car. It sounds like it is pretty far forward on the car, like up by the cats. It only lasts a few seconds, and it appears to go away as the butterflies close for the active exhaust, and only seems to do it on cold starts, not when starting while still warm after running. I've crawled under there, and am not finding anything obvious. I'm probably going to have to put it in the air, cold, and lay under it while starting it to see if I can find it, but I figured I'd see if anyone else had this experience, and had suggestions.