Tested on this server: http://www.gametracker.com/server_info/148.251.3.162:2302/
Fire from enemy AI can be heard, be it standard rifles like Katibas or modded weapons like Ak74/47's
Friendly (sound bugged) weapons still cause damage if shot at me.
Re installing the mods and verifying the gamecache did not resolve the problem
changing hertz and audio-quality on my headphones didnt change anything, as did switching from surround to stereo and back.