http://www.ecollegetimes.com/5-famous-backwards-messages-on-records
“Backmasking” started with The Beatles’ 1966 album
Revolver. John Lennon said one night while smoking pot, he mistakenly played the tapes for the song “Rain” in reverse and liked the sound. So the band began recording messages in
Revolver that could only be deciphered when the record was played backwards. (One such message appears in “Rain”: “When the rain comes, they run and hide their heads.”)
The Beatles, “Revolution #9”
Backwards message: “Turn me on, dead man.”
“Revolution #9” is weird enough played forwards, but played backwards, there’s something that sounds suspiciously like John Lennon repeating the phrase “Turn me on, dead man.” This message was supposedly part of the whole “Paul is dead” storyline that started in the backtrack for “Strawberry Fields Forever” and carried through (at least for Beatles conspiracy theorists) with things like Paul McCartney not wearing shoes on the cover of
Abbey Road seen as symbols of his secret death.