Your knees crack when you crouch specifically as an audio cue to let you know you've entered stealth mode? This was added when playtesters reported that they didn't know when they were or weren't in stealth mode while moving around. It's also why you grunt when you stand up, to show that you've exited stealth mode.
hey boss i can't come in today it's a sunny day and there's a lovely breeze coming in through my window, yeah it's rustling the branches of the tree outside that's finally bloomed so it's pretty serious
i hate to be that guy, but the idea that gender, sex, and sexuality are ontologically pure concepts that can be rigidly defined if we simply police our language enough (our english language, because of course) is—i cannot stress this enough—a total waste of time. you may as well spend your afternoons teaching a brick how to swim