Audio is such a big thing in games; it certainly adds to the atmosphere.
In L4D1 & 2, a game that I have tested a bit, there is a small, sound-related thing that I really like. It is the random, very rare, yet noticeable sound of a round “misfire”. It is not a real misfire, because the bullet does fly out of the barrel. Rather, there is some sort of sub-optimal ignition, or whatever it is called. (I.e. not all rounds sound exactly the same all the time.) I am not absolutely yerning for this in DB. It is just an example of a small sound sfx that adds to the atmosphere. In L4D1 & 2, it adds to that feeling of “I grab and use whatever rusty gear I find along the way!”
DB tells a story of merch groups that fight over objectives in a contaminated, evacuated environment. The sound loop “This is a restricted area!”, heard occassionally in some map iterations, adds to that feeling. Keep it! Do not hesitate to add more sound sfxs (e.g. geiger clicks, radio broadcasts), imho.