I've spent the last 20 min trying to figure out what the big metal tank looking thing is between the two exhaust tips and visible from the rear of the vehicle. Hangs below the bumper. I thought it was part of the exhaust system. It's always annoyed me a little that its visible and just noticed mine now has a black streak in the middle of it going length wise. I haven't bottomed out on anything and really not sure what its from. Automatic car wash maybe... Dont think the dealer would have done it during the tire rotation. Any ideas? Please forgive my ignorance. I know little at best about what makes an automobile function.