Messed exhaust sound??

[ericem]

Can't remember if I asked what it could be, but um I realized when you drive away and your behind the car it sounds like it's misfiring, like it sounds like those old carb car's with black smoke coming out the back, very clattery and poppy. Inside it's a bit loud too sometimes other times it quiet. Never really looked into it. What do you guys think?? Can a exhaust valve do this maybe?? Ill get a vid of it driving away when I get a chance.