That doesn't sound good. Have you complained to Environmental Health? You should be able to get the noise level measured, and if its above acceptable limits then you should be able to get them to take action.

Note that our Environmental Health in Aberdeenshire work to the WHO limits of 35dB for sleep disturbance, rather than the higher figure of 40dB used ETSU-R-97.

These small turbines seem to be seriously lacking in noise data. I couldn't get a straight answer out of Proven. In our case I'm more concerned about noise for us than for our neighbours who are around 450m away.
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aesmith