Ok, here is my unscientific, but several thousand hours of a crewman in the Navy opinion.
Not once did I ever hear another aircraft's engines while flying, even in close formation.
I flew on A-3s, P-3s, C-121's and C-12s. Never when flying and having other aircraft fly by, or if we did a fly by did I ever hear the drone of another aircraft. Even when having F4J's and F14s go by did I hear their jets.
So I dont believe it should be there.
TIOMHO
------------------
Rick "Firefox" Scott