I have 3off, Hugh Piggott design Wind Turbines at 3.7m dia.
One is Cedar blades, the other two turbines are fiberglass to Hugh Piggotts design.
No Noise from any of them, when close up just a slight whoosing sound.
When under load, charging the batteries, then there is a faint HUM.
The blades don't need to turn fast, they are low RPM, are you loading the turbine?