Why... FotRSU v0.81, of course... Some sound mods will mess with some of the settings in FotRSU. Since it is "beta", we have not tested all of the sound mods for compatibility. We hope to do that shortly - but we are talking computers and mods here, so "shortly" might be a year, might be a month... sorry
OH! Before I forget! Do NOT install the game in the default "C:\Program Files (x86)" folder. Change that folder name to something else. You can keep the Ubisoft folder if you want, or make that the "root" folder, whatever, but if you put the game in the "Program Files" folder, Windows will prevent you from applying mods to the game...