A much earlier example (showing the phenomenon isn't so new) is the famous "Cranberry Sauce"/"I buried Paul" vocal at the end of The Beatles' "Strawberry Fields

A much earlier example (showing the phenomenon isn't so new) is the famous "Cranberry Sauce"/"I buried Paul" vocal at the end of The Beatles' "Strawberry Fields Forever" (1967). It became one of the key ingredients in the fun "Paul is Dead" conspiracy/joke.