Wind turbine noise ? damaging or not?

What you have is turbine blade stall noise. Small turbines with no blade pitch control or brakes need some way to govern top speed or they'll fly apart. Small turbines do this by having a blade design that can only spin so fast before the blades stall and will go no faster. The detached boundary air on the stalled blade surface causes a lot of vibration in the blades leading to noise. Small "backyard" turbines are notorious for this noise in high winds as it's their speed governing strategy. This is why some areas have banned smaller backyard rigs because of noise complaints related to stall regulated designs.

Raymond, yes the larger utility sized designs make a thump as the blades pass but the sound described isn't tower noise. I live in a place with over 400 2MW or larger towers within 20 miles of my house. I know what the big boys sound like. It's a forest of steel and fiberglass.

The sound is part of the physics of wind turbines.

That noise is symptomatic of a physical phenomenon that also places mechanical stress on the turbine. Presumably, if the turbine was designed by a reputable supplier, then there should not be a problem. If you cobbled the turbine together from used bicycle parts, then you may need to worry.

For very large wind turbines; each time a blade passes close to the pylon = the supporting tower, a mostly sub-sonic thump is produced. Your small turbines can turn at much higher RPM, so the sound pitch is increased proportionally. Perhaps that is what you are hearing = likely not harmful to your turbines. Hopefully your installation has one or more ways to limit the RPM, below the RPM that destroys the generator or throws turbine blades. Even with these protections a tornado with 300 mile per hour wind will destroy your turbines , house and almost everything else it touches. Neil

Sound potential, whilst the wind is decrease via the blades, and whilst the blades decrease a rooster. Kinetic potential, incredibly this could kill a rooster. Radio wave, whilst the alternator turns, EM wave comes out. electric powered potential, generally we purpose for this.