Incredibly loud means illegally modified. Even the staccato sound of the engine brake (compression release aka jake brake) is very subdued in a properly muffled

Incredibly loud means illegally modified. Even the staccato sound of the engine brake (compression release aka jake brake) is very subdued in a properly muffled vehicle. This is how they come from factory as it is mandated. Plus the DPF+SCR cats added to the muffling ability and are sometimes all in one.