I mostly want to have durability numbers visible on-screen, and the warning is both loud and jarring when i've disabled it through the mod's options.

update; restarting the game after setting the "warning mode" option to "none" disabled the sound, but it only took effect after restarting the game.

This should work, normally. You need to exit the options screen with the button, though, pressing ESC will not work. Maybe you did that?