T3 has no sounds at all, except dialogue.

It's kinda bizarre watching him move around in total silence.

Which files should I edit to return him to normal?

I have downloaded several mods lately, and uninstalled some others, so can't be sure which one is the source of the problem.

The easiest way would be to reinstall the game. Its next to impossible to track down the source of the problem, especially without saying which mods you installed and uninstalled.

Just copy your saves, uninstall the game, and reinstall. The update it, put the mods that you want back in and go. Your saves probably wont work if they're post-mod and you have removed a specific mod. For example, if you installed USM, made a lightsaber, and then uninstalled USM.

Well, it seems the problem solved itself.

I started a new game to see if T3's sounds played in the Prologue, and they were fine.

Then I went back to my old save, T3 was still silent, but I continued on to another area, fought a few battles, and then magically T3 was fine. Might have been a corrupt save file.