The spell has a verbal component, and apparently, verbal components are VERY loud and obvious. If it can be heard, this would make the Silence spell useless in almost every situation. Want to kill one guard without the other nearby guards noticing? Just SHOUT AT THE TOP OF YOUR LUNGS, create the zone of silence on the isolated guard, run up to him and slash him with an axe, and your good. You’ll just have to hope that the other guards didn’t hear your loud casting of the spell. Even worse, the verbal component is used at the START of the casting, not after the casting. This means that the one isolated guard that you are placing the zone of silence on top of can CLEARLY hear you shouting in the casting of the spell right before the zone’s effects take place. Not even he is surprised by you, and he will probably immediately turn to face you.

Maybe I’m just not being creative enough, but this one small thing seem to make and already niche spell even more niche to the point of being virtually useless.