AC,
You have a point there but in real life, it actually sounded like a steam locomotive.
I lived in Maidenhead, about three miles from White Waltham in the early 60s. This was the last days for the Rotodyne and the last days of steam. The Western Region mainline ran right by the airfield. It was nearly impossible to distinguish the noise of the Rotodyne from that of a King or Castle at speed.