You grow accustomed to certain types of noise. When I lived in the Officers' Mess at Brize we had over 20 VC10s stationed there (10 Sqn and 101 sqn) but only a handful of Tristars. As a result, we heard many more VC10 movements and so became used to them. I could sleep through the ZeroDarkThirty Dulles and Deci departures (on the days when I wasn't driving either) but would be woken by the much quieter Tristars because they were a relatively rare sound.