From Mind Hacks:
... psychologist Konstantīns Raudive ... began to believe that he could hear the voices of the dead amid the hiss of radio static – after, it must be said, much re-recording and amplification of the samples. ...
... but subsequent scientific studies found that everyone was hearing something different amid the static, making it one of the most well-know examples of illusory meaning or pareidolia of its time.
Listening for the voices of the dead
Pareidolia is also involved in claims of "backward masking." I have heard "Stairway to Heaven" played backwards at least 15 times in the course of an afternoon by a guy who insisted that a certain bit said "We love you, Satan, Satan." I heard no such thing in the noise, but only the sound of backwards singing.