It has been said that the soot is a result of direct injection.

 

Finally had some time off from work and school, so I called around to several local muffler shops and was amazed at the price differences for just cutting off the muffler and welding in a new one. Using the same Magnaflow muffler ranged from $140 installed, to one place asking $240 installed. I went with a place that has been around for quite some time installing mufflers and is part of the BBB for $150 and they let me watch the install take place. The factory muffler is huge. The installer joked that it looked more like a gas tank than a muffler. Anyways the welded the factory hangers onto the muffler along with the factory tip, and sounds very nice. I decided to keep the factory resonator in place, as was their recommendation as well. Sound is deeper and seems like I can hear the turbo a bit more than with the factory piece. At higher RPM's on the freeway it is noticably deeper and a bit louder, but not by much. Nice mild improvement.