My muffler seems to be absolutely full of carbon. When I tap on it it has a very "solid" sound. It also spits a bunch of black carbon out when warming up and the edges of the tailpipe are jet black. Is the muffler in need of replacement or is this normal? Also, how loud compared to stock is the 40 and 50 series Flowmaster?
By the way I have about 77k miles on a 2001 4.0 with manual tranny.