Go to your Data folder usually in C:\Program Files (x86)\Steam\steamapps\common\total war shogun 2\data
and check that you have a file sounds_fixed.pack with date 29/9/2012.
If it has different date then somehow your installation is messed up. Uninstall->Install again the mod.
Also if you use another mod, probably a mod that adds units, then this will not be compatible and will mess your sounds when used with DarthMod.
PS. The audio fix file is also available here: AUDIO FIX (YOU NEED IT FOR THE STEAM WORKSHOP VERSION).
Many report sound issues but they do not use this file as it is advised.
I know that SW version downloaders are more than those who have this Audio Fix file.