Tuning exhaust sound is quite a science, and it starts with custom-crafted exhaust headers, which replace standard-issue exhaust manifolds coming right off of the engine. Serving as the vocal chords of an engine, headers typically equalize the length of each tube coming from the cylinders en route to a collection tube prior to the catalytic converter and the remainder of the exhaust system. Acoustic and powertrain engineers spend countless hours perfecting every bit of the exhaust system to find the balance between a healthy burble and an annoying drone.
As to unwanted noise--the kind that interferes with the engine's song or your conversation with your passenger, such as wind noise or excessive intake whoosh--engineers must design this out of a vehicle to avoid perceptions of crudeness, thrashiness, or cheapness, not to mention driving a relentlessly noisy car contributes to driver fatigue and annoyance (I can attest, having fitted a droning glasspack to my 1988 Honda CRX that set off car alarms in parking garages across Atlanta).
To eliminate the nasty stuff, Ford engineers paid attention to the most minute details. From the design of the windshield wipers, the location of the radio antenna, and the thunk of the doors when slammed, they went over every sound generated by the 2010 Ford Mustang with a fine-toothed comb in an effort to produce sounds pleasing to the human ear. Sound-dampening materials were fitted to minimize unpleasant noises, and conversely, Ford's Induction Sound Tube technology actually pipes the good stuff from the Mustang's induction system right into the cabin. BMW used this technology to good results in the most recent Z4 roadster, highlighting the fact that too much isolation, especially in a sportcar, results in a bland, detached experience that is a sure turn-off for enthusiasts.
It's great to see domestic manufacturers delve into the details, as this is precisely the area where foreign makes have trounced them for years. Import buyers typically love (and fall in love with) a car's details, and perhaps with increasing dedication to improvements in the subjective elements of a vehicle--textures, sounds, materials, "feel"--domestics like Ford will continue their quality improvements with a concomitant improvement in market share.--Colin Mathews