This is an interesting article on noise issues regarding wind farms. One conclusion is that by raising the cut-in speed, i.e., the wind speed when the turbines start spinning, the perceived noise is greatly reduced. The amount of power produced at low wind speeds is so small that is often not significant financially.
Some of the comments discuss various decibel (noise) readings, and what is acceptable. I guess I have to find a dB meter and start measuring. Anybody have one?