I can't figure out why but all of a sudden, after the most recent automation update, it stopped recording the sounds for my Automation cars were just nonexistent. I did check in the mod file and under Document/\BeamNG\mods/insert car name here/art/sounds only the blends folder was there, no engine folder like the other cars beforehand.
As of yesterday they fixed it in an update for Automation, so newly exported vehicles should have their sounds back