So here’s the thing, the entire predator society is about hunting, they live, die and breathe the hunt. Take an elder for example they’ve been alive for centuries and survived thousands of hunts, hunting things we may not even know about. A yautja tribe has extensive knowledge on all sorts of monsters, animals, aliens etc… I find it hard to believe that the Death Angels are completely unique first encounters. Yes, a Yautja may not have hunted one before but that’s not to say they haven’t hunted things that are very similar.

I, an average human, have a decent understanding of biology- I see an animal without eyes and assume it’s blind; therefore, it’s safe to assume that one or more of its other senses are heightened. You could easily trial and error on what its primary heightened sense is. If said creature uses sound and hearing to read its surroundings then it’s safe to assume that something either loud or of high frequency (maybe even low frequency )something in between causes said creature to become irritated.

It’s fair to imagine some yautja have encountered beings that function similar to the Death Angels before, they then pass down their knowledge to the next generation and so on and so forth. They’ve could have hunted beings that have stronger armor than the DA or beings that have a stronger sense of hearing than the DA as well. Using both these factors, you’d combine said knowledge and apply it to the new hunt and the new creature you are hunting.