Even if they are handled client-side... with the right function in orpheu (or even ham)and the right predictions when the sound would be played, you can block that by changing the required conditions to be played...
we know the server sends whenever data to clients like player is shooting a weapon and how many bullets the weapon has... you can modify that sent data in the right functions maybe addtofullpack either way u can block the sound if the conditions for it to be shot are right by making them wrong and playing your own sound... no?