This wind turbine is silent and high efficient. It’s callet Energy Ball.
The Energy Ball uses the Venturi effect, a measurement of pressure created by forcing incompressible liquid through a restricted section of pipe. The Energy Ball channels air through six blades, accelerating the speed of the air as it blows around the rotor hub, creating higher efficiency and lower noise levels. It is also effective at low wind speeds.
Due to the unusual and exceptional aerodynamics characteristics of the Energy Ball, it creates a wind flow pattern that converges first and is then accelerated through the rotor, resembling the rapids in a river (the so-called Venturi effect). This translates into a higher aerodynamic efficiency compared to conventional wind turbine designs.
source: EcoGeek and HomeEnergy