Beginning in January 2014, Lufthansa will start retrofitting its fleet of 157 Airbus A319/A320/A321 aircraft with Vortex Generators that will reduce noise levels by approximately 2db.
The Vortex Generators will be installed underneath the wings which will cancel out certain sounds that are generated when air passes over Fuel Tank Pressure Equalization Vents. Currently, when air passes over these vents it creates an effect and sound similar to when you blow over a bottle top. The new vortex generators will create a mini-tornado effect over the vent and eliminate the sound effect.
According to Lufthansa this will reduce the exterior in-flight noise levels by up to 2db so that the aircraft will generate less noise pollution when landing and departing an airport as well as when flying overhead.