Ther are about 10 "sound" buttons/keybinds.
Are you talking about the master audio toggle?
btw: I checked the sweetFX stuff and it is not using variables from the ESO game itself, so I hardly wonder if this could have to do with any addon inside the game.
Ok by the source code of AudiControlDoctor there does not seem to be any point why it should interfer with SweetFX.
So it has to do with the keybinding you are using somehow.