Date- 6th April 09 Source- http://www.nasa.gov/multimedia/podcasting/index.html 'Air transportation is vital to our economic health and quality of life, but that prosperity comes at a price: noise pollution. Many components of an aircraft contribute to noise pollution, particularly the nozzles of jet engines. The exhaust gases exiting the engine through the nozzle are a significant source of noise, particularly on takeoff. Nozzles produce hot, high speed air that contributes to thrust. This air interacts with the ambient air cooler, and traveling at a lower speed. You can hear the result..'