What if when within a set distance from a secret/breakable thing, listening/meditating made one of your teammates say a thing? I feel like just making flowing air or the like wouldn't help unless people knew that that sound meant that thing, but having a teammate imply that there's a breakable wall or something more to that room would show that a thing is there, while not directly showing where it is and spoiling the trick to get there.
Also, if you do any kind of thing to indicate that there are secrets, it seems like it could be frustrating if you don't have the powerup to access it yet. Like, in the prototype, if there was an indication that there was a breakable wall towards the beginning where the first secret was, I would have sat around there for a while looking for it and got frustrated when I couldn't find it. For fear of this, I would rather not have indications. At least, not until after I have every secret-getting powerup.