[Steeveedee]

FWIW, I've seen brand new cars with broken baffles in the muffler. I'm not saying I'm right, it's just something to check. After seeing geezer#99's post, it occurs to me that you could use a mallet and tap the pipe and muffler to see if you can duplicate the rattling noise. I found a case where a car had the oil light flash when doing hard braking. Turned out that the oil pickup screen had fallen off the pump. I hit the pan with a rubber hammer, and could hear the screen plop back down onto the pan. That's one rare failure, right there!