So my *new* 2004 coupe has this wierd rattling noise, only when its warming up. When I start the car it sounds beautiful, nothing noticeable, but after i slip it in reverse and hold on the break pedal, there is this pretty loud rattling coming from my back end. I'm not too sure why this could be but after backing up and putting it in drive, its gone? I know there's a ton of rattle posts out there, but has anyone diagnosed this one?? Before I just dismissed it, but lately Its kinda driving me crazy up in her'

 

had it since new on my 03. on mine, its a heat shield above the muffler. Havent bothered to fix it. By the time I reach the dealer, its warm. I dont care to leave my car there long enough for it to cool down and rattle.