I don't believe there are enough helicopters in the area for a steady string of traffic.
Tony - do you have a petrol lawnmower? Now they really get on my nerves - it can take hours for my neighbours to cut there lawns and its just relentless.
Perhaps your neighbours are the same?
Next time you see a helicopter try thinking positively about its purpose as listed above - day dream about where it may be going. And before you know it the thing will have gone and the noise no longer there.