Grease, LOL, they had a show on tv showing them making the three propeller design, bearings run in motor oil, I think there is a built in pump in the transmission at the front.
Couldn’t resist.
We have hundreds of them down here and I’ve never heard any type of noise from them and as slow as they turn, birds would have to be pretty stupid to fly into them.
They sure screw up the skyline though.