I have a deep, instinctual fear of the sound that Husks make in ME2. It terrifies me so much that I get scared before it even happens, and refuse to move forward without having both of my squadmates and a combat drone ahead of me when I know there are going to be husks.
They are terrifying, relentless, and the fact that they feel nothing and have no concept of fear or pain... it's horrifying. They don't stop until you destroy them. They don't act like anything you have ever come across, and although they look vaguely human, they are devoid of humanity. Husks are a violent, vicious emptiness that you're forced to look into as you race to destroy before it surrounds you and beats you to death as you struggle against it. The noise they make is a hollow, empty moan that almost sounds familiar, like it could be grasping at life. But it's not, they're not grasping at life, they're grasping at you. No purpose, no feeling, no concepts, no thoughts, no emotion, no drive, not even instincts. They are nothing. Their groans are gaping, empty, meaningless sounds. No thing is as terrifying as nothingness, how can you bear to look into something that does not look back, cannot look back, has nothing to look back with? It will not react, it does not stop, it cannot yield. Their howls consume silence, swallow it, rip it from you.
They are my worst fears made manifest. And their noise is enough to get me all poetical, so that's pretty damn scary.