Yeah. I don't know enough about the workings of air systems to know what happens up there but in a big building especially, there's got to be some kind of something moving the air where it needs to go, hopefully without more noise than necessary. (Haha, unlike our bathroom fan designers who seem to think-- Oh, but it is so small -- let's make it noisy so they know it's working(!) Lol.) Anyway, that's also a sort of sound the people that work there would be unlikely to notice, being so much a part of the daily environment as to be.. tuned out, you know?

Just guessing.
Whatever it is, hope your mind can mellow and get in sync up with your body so you can get some nice