A huge difference. If you have turndowns after the muffler, the sound waves tend to bounce of the ground and reflect into the floorpans. You hit a certain rpm and the wavelength of the sound matches the natural frequency of the car's body and BINGO!!! You get this wonderful thing called harmonic resonance where the entire car is vibrated by the sound of the exhaust causing skull cracking, migrain inducing, teeth grinding noise in the cabin.
