Right, but do we really need a “don’t make a bunch of noise” action? You could just say your character is being quiet, and not take any actions that would make a bunch of noise.
Well, that is part of the issue. Whenever someone tries to move quietly, they hope they are, but cannot know it. If a sentry is looking down a hallway and I want to cross an intersection behind him, I am already out of his line of sight. Any "hide" check is to be quiet, not to be unseen. I focus entirely on being quiet, hope I am, and that he doesn't just turn around stretching or something and sees me.
When I was just starting college, as a lark, we had my girlfriend go to her living room, sit in a chair, and close her eyes. We each then took turns trying to sneak through the room without making any noise. The TV was on, but at a lower volume, to simulate people talking nearby. If she heard us, she would point in the direction of the noise. If she pointed at the person sneaking, we told her and she "won". If she pointed but was wrong, we would say nothing and the person sneaking continued. If the person managed to make it across the living room without alerting her, they "won".
Out of the six of us, only two made it. Now, one was close, the other three a bit more clumsy, etc. It isn't always easy to sneak if someone is on the alert--such as a guard should be.
So, the rules focus a LOT on the unseen aspect, but want you to be out of line of sight (makes sense) but then also have three-quarter cover, total cover, or be heavily obscured. Well, if you are Heavily Obscured, LoS doesn't matter (barring special circumstances maybe) and Total Cover seems to imply (?) you have an obstacle completely covering you... so there is no LoS, either. With 3/4-cover it is a bit odd... can they see you? Is there LoS or not???
Generally, other than 3/4-cover, you are "unseen" in all the other options---so what are you rolling for in those cases if not to be quiet???