Growing up next to LHR in 50s and 60s one got very attuned to the many different engine sounds and could be very accurate about guessing the type from the noise . Even able to distinguish different type same engine, Comet /Caravelle for instance.
Ditto. Our house was under the approach path for runway 28L. Other distinctive engine tones: the crackle of Wright turbo-compounds on Super Connies and DC-7s and the low-pitched whine of the Centaurus on BEA's Elizabethans.
Our TVs also served as aircraft detection systems: before the engines could be heard the TV picture (405 lines, black-and-white) would start to fluctuate in brightness (presumably as the signal reflected from the approaching aircraft interfered with the ground wave). As the aircraft got closer the fluctuations would increase in intensity but slow down in frequency, eventually to a constant brightness. Then the sequence would reverse as the aircraft flew on towards LHR.