So far, I have only found one area when the Silence spell worked at all. Does not Silence
* Goblin princess - she still calls for reinforcements
* Goblin war-drums - still calls in more goblins
* Cracked wall - goblins still hear the racket
* Hook horrors - still call for alarm
However, in casting Silence on the Hook Horror that surprised jumped into my party, Silence DID work on all my surrounding party members.
This should be a much more useful spell.