A W Smith
Philosopher
The background noise in manhatten on 9.00am 9-11-01 would have been phenomenal, roaring fire in wtc1,numerous sirens,speeding firetrucks,normal traffic,crowd chatter would easily mask the sound of approaching plane until the last few seconds which would reach observers after the plane had struck the tower due to the slow speed of sound and was drowned out by the crowds reaction to the impact.
with flight 175 flying toward him at high speed. He would hardly notice the sound. Until it passed for that brief half second before impact.