I bought a used 2004 2500HD with the LB7 engine. I have a couple of questions though...the muffler is kind of loud and I was looking and noticed that there is no cat on it. Did this engine come from the factory like this? Also is there anyway I can quite it down? I'm not concerned with the power gains of the aftermarket muffler, but don't have any idea where to get a factory muffler without going to the stealership. Any ideas??