It tends to happen during Episode 3 when things are supposed to be quiet. I played Episode 1 & 2 before the Episode 3 update, but didn't notice it then. The most noticeable one is in the living room in Tarissia (tarissia_living_room.ogg). It kind of sounds like the AC is on full blast.
There are a few other spots where there's kind of a similar constant sound. I'd have to go through Episode 3 again to list the specific scenes.