First was an Eoltec Sirocco at Burray Community Centre. (We noticed they'd positioned it a good way away from the buildings!). There were two types of noise apparent. From a distance, beyond about 30m or so, there was the swishing of the blades. Close to there was also a sort of growl or hum. I'm not sure how to describe it, but a very mechanical sort of noise which rose and fell with the wind strength. Because that turbine's in quite a noisy location by the road, at first I thought it was something like a four-stroke motorcycle in the distance. In my opinion that noise would be very disturbing, but it appears that it isn't audible beyond 20 or 30m. Unfortunately we couldn't check out the downwind noise without trampling the man's barley.
Next a Proven 6 on (I think) 9m mast at Kirkwall Squash Club. The wind was stronger. Close to the machine makes all sorts of creaks and groans. Further away the blade noise dominates, making quite a solid beat very different from any natural wind noise. We could check downwind at this site and I reckon you'd need to be around 125m (150 paces) before that noise was acceptable to me.
Unfortunately we weren't able to check out any of the other installations due to lack of wind. An Eoltec on Rousay was stationary when we passed it, but I note that it is quite close to the house and near to neighbours as well.
Interesting all the same. I was surprised how intrusive the Proven blade noise was, and both these machines were on sites where background noise especially road traffic is greater than at our place. At this stage I can't tell whether an Eoltec would be any quieter, so for ourselves it looks like we need to find a site at least 125m from our house - much further than I'd hoped.
Also of concern is that clearly we both found the noise annoying even at levels that Environmental Health would say is OK. Apparently in Aberdeenshire they're happy with the Proven 6 within 75m of neighbours.