Watching First Duty - Ship noise at Starfleet?

Just watching First Duty, DVR'd from BBC-A and noticed in the scene where Locarno is talking to the other cadets before the inquiry, that the TNG sound mixers laid in the classic engines 'ship rumble' noise behind the scene, as if they were on a ship, but they are on Earth, no reason to have louder than normal room tone.... perhaps even birds chirping from outside or something.

Just an observation...

 

The building has a warp/impulse reactor in the basement.

 

Wesley had one of his experiments in the closet.

 

I've never noticed that, I'm going to have to watch it now. I've always found that sound quite soothing though. Maybe I should record it and play it in my room at night!?