My coach has an AFE oiled air filter and an aftermarket muffler. The conical shaped air filter is removable from its metal cylinder, cleaned with a detergent spray, rinsed completely, let dry overnight, then re-oiled before replacement in the metal cylinder. The whole metal cylinder is removed from the engine compartment before the filter is taken out of the cylinder. I have no idea what the muffler is. As you noted, I am also told the engine exhaust noise is pretty loud when accelerating and even louder when the jake brake is engaged. I can notably hear the exhaust noise under acceleration and jake braking if a side living room window is open. Otherwise, I cannot hear it much. I am aware that heads turn on the roadside from the noise as I pass by. I always comply with the "No Engine Brakes" signs when entering cities.