ns1 has proven that sound is a very important component of gameplay. especially for the marines. not hearing a thing makes them half-blinded. and its not much diffrent @ns2.
so i just thought it could be a cool features if hives (or another alien struc, maybe a lifeform?) had the ability to make nearby marines deaf for a few seconds (just hearing a loud "beeeeeeeeeeeeeep" meanwhile)
while the affected marines cant hear a thing, the aliens stand a good chance to ambush them or sneak away