Yeah I understand, though my intention wasn't to have this as a warning of an inevitable base attack, but just to add a bit more realism, and "ear candy" to the sounds we already have in AH.
Sort of like my wish to hear the 8in zooooooooooooooooom over your head while in tower/gv/gun

Perhaps have a multiplier for this engine noise? So if you have x planes within a certain radius it increases the overall radius that the engine noise could be heard from.
I believe it's 3k-3.5k right now, so if you had 5 planes within 500 yrds of each other, then it increases to 4k or more. And, the more planes that are closer together, the louder it gets when you fly near them (or they near you). Obviously, there would be a cap on the distance to engine noise, and loudness ratios, otherwise you would hear them 10k+ away, and destroy your speakers .

While not necessary I think it would be cool.