So the other day I was driving (08 WRX) and all of a sudden it sounded like my muffler fell off. So I pull over and have a look. Still all there as far as I can tell. So now the car rumbles mostly at idle, but occasionally when I'm driving, too, although the sound typically goes away the minute I hit the gas. My friend thinks it's a baffle and the whole thing needs to be replaced. I hope not, what do you guys think it might be?