Zappomatic, where are you standing when you say you're behind te building? Do you mean south of the building, on the ground? Because I've been beside and behind the building while the turbines and not heard a thing. Or maybe you're in the apartment underneath the turbines, having paid £££ for your apartment?
Or perhaps you do actually have a box of demented frogs about your person? :)
The bearings will become noisy. As I've posted previously the engineers who put them in reputedly give them a life measured in months not years before the bearing noise is unbearable in the building. Presumably explains why they're running only one turbine at once, only occasionally. Should last for years that way!
We get a good view of the turbines from our place. Hardly ever see them turning, and generally only ever see one turning at once. Saw all three going at once a week or two back, which was quite remarkable.