I was playing DayZ standalone with my buddy last night (13 Mar 2018) on a community server that, to our knowledge, does not run any mods. During out play, I realized that whenever my buddy fired his USG-45 the gunshots would not sound. He did not have a suppressor, and he was often right next to me when he was firing. I could hear the bullets flying and impact, but his USG-45 never once made its own sound.
My buddy could clearly here my KA whenever I fired it, however.
I am listing this as a major bug, because PVP happens, and if I were shot at by a player using this firearm, even unsuppressed, I would be at a significant disadvantage for not being able to hear them.