Living for many years in Camberley ie between Wokka world at Odiham and London Chinooks were always scooting up and down the M3 and very noisy -I would have been mostly off to one side. But is there any helicopter that's quiet? Where I live now, there are occasional Apaches and Chinooks plus assorted smaller mil types , Merlins etc, on their way to the various military bases or Yeovil? and then there are private ones which can be heard miles and miles away .
I am old enough to remember Fairey Rotodyne-now that was noise , Ospreys are incredibly noisy and someone has mentioned the A400 whose strange musical tones are a regular occurrence as they head out from Brize towards the southwest, a lot more conspicuous than the Hercs which were close to inaudible until right overhead especiallyat low level -