As of right now, there is nothing in the vents, and that sound comes from nowhere just to freak you out. Seems to be doing its job. We can SPECULATE that it may have something to do with spring trap given the teasers they've shown in the campaign and the new night guard design reveal trailer where you see the creepy Springtrap hand. But both of those are guesses. I dread the day that they add spring trap with a creepy model, and even moreso the day any of the AI can get into the vents. I'm sure the regular AI we have now won't enter/be able to enter the vents due to their.... physique. But there's no telling if mechanics will/won't change in the future with new AI. That, and it would make the breakroom one of the only safe places left.
As it stands right now break room and I think the room with the chair, and possibly the electrical room are the only ones that are not patrolled, but all of them will be entered if they hear your companion distraction in said room. I've tested it before and noticed that luckily being in the locker in the break room will actually hide you from animatronics even if you lure them in with the companion. I hope it stays that way because TBH once I've done the tasks I don't like the idea of having to spend the whole night running when I can just hide somewhere and do something on my phone while I wait it out. I'd rather have fun mechanics that encourage me to play the night through, but unless they change it to where getting caught is not an insta-loss I'll have no interest in running around when I don't have to.
