@razazel I'm having this issue too!
a 100% way of reproducing it (for me at least) is to place down a helicopter in the editor and start it up. If the engine sound is in the idle mode (the one that you hear all the time when you fly around) press ESC and click on abort. After that, the sound is bugged and you can hear it until you restart the game. This works with several instances of the sound as well (If you reproduce it several times).