What type of noise is generated by wind energy turbines?

Wind energy turbines emit sound.  The advances in technology make the sound heard from the turbine almost undetectable.  The main sound being the smooth swoosh of the blades passing over the tower and some sound from the mechanical gearing when the turbine rotates.  Strict manufacturer guidelines allow for noise emissions to either meet or exceed residential and municipal ordinances.  Siting, ground cover and ambient noise all affect the decibel (dB) level heard at any given time.