Your 12288 is the same design as my 12388, except that mine is 6 inches longer. Mine is louder than the factory muffler, no question about it. How do you compare yours to the factory muffler???
As quiet as stock, if not more, at start up.
Cruising, not much difference.
WOT, a little louder.
I guess I'm used to a deeper rumble and having the engine let me know it's there.