Ok sometimes whem im in a stop sign my muffler rattles, making an odd noise like a rumblin noise and it feels like the car is going to turn off, it also idles loud then it goes away also when the car is cold in the morning and I take off it makes a rattling noise it sound like the cat, but I just replaced it and I got my whole car checked out at midas and they said my exhaust system is fine it could probably be the after market muffler when I got the car it has a bootleg aftermarket muffler that makes noise,