When standing in water and shooting the player cannot hear the sound of their weapon fire. I tested on Tanoa, Malden and Stratas and all were affected. It affects both modded and vanilla weapons, with mods active and without mods active. If you are using the SDAR (diver's weapon) you do get sound but it is the underwater gunfire sound.

I am playing the dev branch and have not tried it with the current release build.