So my idea is pretty simple, if you shoot a gun, and you are not used to shooting it (Lets say you have a job that doesnt use a gun) you get a temporary ringing, and the more you shoot your gun. the less it rings.
Another idea is that lets say your in multiplayer, and someone shoots a gun right next to your ear. You will either get the hard of hearing trait, or if your unlucky. You become deaf.
Seems like it could be a good idea, and it gives ear protection a real use.