I been looking for this and I found it a while back on a fix for no sounds in GSX on FSX, but the link for the fix is no longer active.
Last week, I reinstalled my Level D 767. Up till then, I had all my sounds in GSX. After completing a flight, I started my next and had nothing. No warning beep to close a door, no sound from the ground controller, no sound of passengers coming on board, no sound of the food cart rolling into the aircraft during the catering service. I do have the latest version with all updates, including my graphics and sound drivers... but like I said...it was fine till last week. I honestly don't know if the 767 had anything to do with that.....
Am using FSX, Win 7, and the no sound happens with Level D 767, PMDG 777's, PMDG 737.
Thanks...