Are they? I haven't noticed the sound myself, although I don't live next to windmills and just travel in areas with wind power from time to time... I also grew up next to train tracks and now live next to an interstate near an airport so may have a high tolerance for background noise!
There is one turbine near where I live in Scandinavia that is very noisy. It is a low thumping sound that penetrates houses and is horrid. Those living within a km perhaps more won a court case to remove it but the owner has appealed and appealed and during the years or appeals the thing keeps turning and keeps being noisy so people can’t sleep. My understanding is the simulation and calculations of the noise that were part of the planning process were flawed and did not accurately model the terrain.
Meanwhile, not 5 km away, there are a bunch of turbines with people living around them and no problem.
So the exact slopes etc of the terrain is very important.