Get your cans (headphones), put on 'Dark Side of the Moon', go to very last track (Eclipse) and fast forward near the end (heartbeeps and shortly after the spoken words, "There is no dark side..."). NOW, CRANK IT UP and you'll hear an audio seepage of an instrumental that is NOT by Pink Floyd!!
A long time ago, I happened to hear it but couldn't place what the tune was. I knew it was an orchestra and really sounded familiar. Just to get to the point, it's the Beatles' rendition of "Ticket to Ride" by ?
IMO, it was a mistake and probably picked up from another studio (obviously, the walls aren't so soundproof). It could of been picked up in the control booth, (accidently) sent out by audio talkback in studio and picked up by mics.
Someone had this theory that PF did it intentionally as a homage to (Beatles) - hence, Abbey Road (same studio), etc. IMO, I don't agree 'cause why that tune??
You can also hear seepage in Van Halen's "Eruption," especially at the end.
Ant