They're certainly not silent, but unless you're actually standing right under one they're rarely particularly noisy. Modern ones should be about 35 decibels at 300 meters distance. You're never going to hear an offshore one, really.

They're most certainly not silent! If you're standing right under one, you can hear it over car traffic and the breeze! (Well, unless the wind is blowing really hard: then the wind might be louder than either, considering the usual minimum distance between wind turbines and roads.) Whatever will you claim is silent next? Refrigerators? Lightbulbs?