It depends

How about that answer as vague as this law:
Texas Laws on Exhaust Sound Limits | eHow.com

MANY diesels do that since there is a turbo to 'somewhat' muffle the sound...
but just roll down your window and listen to the 4 cylinder ricers and how pitiful most sound with their little fart cans sticking out of the back...

And nothing sounds as 'wanna be but not there' as a six cylinder chevy pickup without mufflers !!!!

but depending on your engine, you may benefit from a mellow sounding flow through muffler like the walker big truck muffler...

We put magnaflows on the wife's Audi 4 cylinder turbo, but they are very sedate, just enough to give it a LITTLE rumble, but not 'noise' !