Wow, even though this post is dead and you are long gone, I feel compelled to help you DGM. Somebody should have helped you.
I had the same problem. Basically, you forgot how you used ShockEd.
When you open ShockEd it automatically loads up your gamesys or whatever you assigned it to load. For some reason, if you open the program and then have it open the same .gam file it gets corrupted.
Symptoms include:
1. If you Multiplay players will have really funky looking IPs (They will still work, though.)
2. When doors open they make no sound.
3. You can't hear footsteps. Or weapons. Or hitting with said weapons.
4. You can still hear monster cries.
Reinstall the ShockEd and make sure there is a fresh gamesys in the folder with it. Open the program. Don't open the .gam. Just start editing. But remember to save, for it doesn't do THAT automatically.
You probably already solved it a long time ago, far away. You've raised a family now and rose to the top of your career. Godspeed DGM. Godspeed.