I saw the link to this BBC story about efforts to build a quieter airplane on the DefenseTech.org site. It does so with a flying wing airframe and engines which are above the plane and which direct their noise upwards. But, while the military potential is obvious (noise stealth), the civilian purposes for which it is being designed are too.
The decision to shut down Stapleton Airport and build Denver International Airport, far from the central city (and to close Lowry Air Force base entirely), was driven in part by noise. Residential neighborhoods and noisy airports make poor neighbors. Even DIA has to pay compensation to neighborhoring jurisdictions because of noise violations.
The result is that someone like me who lives in central Denver has to drive 45 minutes to the airport each way, instead of fifteen minutes. When your dropping friends or family at the airport, that is a one hour difference in the round trip travel time. In contrast, if airplanes can be built quiter, cities can again get closer to the airport reducing that impediment to flying caused by the long drive. From a New Urbanist's perspective, less driving and cities more connected to transportation networks other than personal automobiles is always a good thing.
It is an idea worth keeping an eye on for its implications both military and civilian.