Living close to the home of the RAF's 'Wokkas' (Chinooks), the first sign that one is on its way over, is when our lounge door starts resonating. This can be a considerable time before the Wokka can be actually heard.
Mechta Minor's first word for anything that flew was 'Bop Bop', which was obvious to us, but less so to others, especiallly when the aircraft wasn't a Chinook, or even a helicopter sometimes.
Some Chinooks make a very strange slapping noise which sounds like they are about to fall apart. Those in the know reckon it is just the blade tape coming adrift and is nothing to worry about.
If you think of a Chinook as a 9000hp loudspeaker at 675Hz (225rpm rotor) then you can appreciate why the ground shakes.