I’ve had an instance where a Siren made one of it’s hissing sounds that sounded like a woman, not like other Siren sounds. Like someone had recorded the sound but not applied effects to make it “alien”. I can’t remember for sure but I think it was when I attacked or killed it.
Has anyone heard this also?
I haven’t had sirens sound like humans, but I have noticed poisonworms having human screams when killed. Several times.
Hmm, I always had the “squish” sound when killing worms. I guess this would be more off-putting then on the siren 
That has since been removed by an update.
Come to think of it, it hasn’t happened in a while. 
At the time, I thought it had something to do with the type of weapon interacting somehow - I was using the NJ pistol and later on I’d mostly killed worms with crossbows and virus rifles. I figured they might have had different death sounds depending on type of kill, and some file path got mixed up.