Track Playbacks - No Engine Sounds from Enemy A/C
 

Anyone know why I'm not getting any engine sounds from enemy bombers or fighters when viewing track playbacks?
All other sounds seem to be in place during the playback; pilot chatter, allied engines & gunfire, vehicles, explosions etc. Trying to make a little video & it's proving very awkward with 'silent foe' ;)
All sounds are present & correct during the initial mission I might add.