Flows's are louder in the interior yes, but drone is a certain tone that gets emitted, its not 'noise' or 'volume', and it is caused by more then just the mufflers (although they certainly play a big role), everything from the engine, came, headers, and pipes are going to effect that. I don't think a lot of people get the difference between drone and interior noise.
every car is different and every ear is different.