I just did something like you want while messing around with FPSC . A monster keeps making strange noises randomly all the time till it's dead , isn't that what you want ?
but what makes me doubtful is that you didn't think about the random=x condition (pretty obvious lol) so I'm not so sure if that's what you want .
anyway hereare the lines :
:random=600:sound=audiobank\voices\zombie_007_16.wav
:random=600:sound=audiobank\voices\zombie_019_16.wav
"I am the night visitor when everyone is sleep , and when the last light fades"
The illusionest