Yes and no. You can make your own sounds and implement them into a mod, but right now your mod won't pass the consistency checks - so servers won't let you join. I don't know if UWE is planning something in that area.
To learn how to make a sound mod anyways, check this thread, second post (chapter 4):
Comments
To learn how to make a sound mod anyways, check this thread, second post (chapter 4):
forums.unknownworlds.com/discussion/128106/how-to-make-a-mod-for-natural-selection-2
Have fun!