I know, the game over sound is cool--I agree. I find the "death thump" a nice slap on the ass following Geralt's reaming at the hands of his foes, too, but when I play with headphones, it's just too loud. This very simple mod mutes that sound so that it doesn't reverberate through your skull as you wait for your previous save to load.

On request I've also made another mod that silences the "load thump". You can use either or both of these mods as they modify separate scripts.

Install:
Place modNoDeathThump and/or modNoLoadThump into the \mods directory of your game installation directory.

Uninstall:
Remove modNoDeathThump and/or modNoLoadThump from the \mods directory of your game installation directory.

modNoDeathThump includes the following file:
/content/scripts/game/gui/menus/DeathScreenMenu.ws

modNoLoadThump includes the following file:
/content/scripts/game/r4Game.ws

If you use another mod that includes either of these files, you'll need to merge the changes from this mod yourself, either manually or with a merge tool. I can't vouch for Script Merger, but I imagine it would work fine. However, my changes are simple and it should be easy to manually merge them. Any script merge errors are a problem on your end and are not related to the mod--please don't post about them.