It originated from the Sgt Pepper LP, the noise was put into what is known as the "lock groove" at the end of the record. Since the lock groove is designed to repeat infinitely (so that the needle is not damaged by running over the surface of the center label), the Beatles decided to put an infinitely looping clip of bizarre sound in there, beginning with a high-pitched sound that humans are unable to hear. John Lennon supposedly did this for the sole purpose of "irritating the listener's dog".

"A Day in the Life" is the song by the The Beatles that appears as the final track on their album Sgt. Pepper's Lonely Hearts Club Band. Wikipedia has this to say on the matter: On "A Day in the Life" as the song ends- "Immediately following the dying moments of the crashing piano chord is a tone too high-pitched for most human ears to hear, but audible to dogs and other animals and most younger listeners. Lennon's alleged intention in inserting the high tone was to irritate the listener's dog. The crashing piano chord and 15 kHz tone are interrupted by a loop of incomprehensible Beatles studio background noise. Spliced together at random sections, some of the snippets in the loop would play forward to be heard as, "Never could see any other way." Others were played backward as "Will Paul be back as Superman?" This lasts for two seconds and the final three syllables are on the final groove, creating a loop that is repeated endlessly. This noise was placed in the concentric run-out groove of the vinyl LP. If the listener's record player had an auto return mechanism, a short burst of noise would be heard before the needle was lifted and moved back into place. If the listener's record player had to be returned manually, the sound would loop infinitely, leading the listener to wonder if something had gone wrong with the record or the record player. This was mainly due to the practical difficulties involved with manually spooling the record backwards while maintaining a constant speed."

it was meant to say something about the devil, backwards? thats what i heard anyway ;)