The Beatles’ song I Feel Fine marked the first time feedback was deliberately used as a recording effect, later to be used by a lot of musicians as a special effect but perhaps most extensively by Jimi Hendrix. The Wikipedia entry for the song says:
The intro to “I Feel Fine” starts with a single, percussive (yet pure-sounding) note (a high “A” harmonic) played on McCartney’s Hofner bass guitar that sustains, perhaps beyond any song previously recorded. It is then transformed and distorted via feedback.
According to McCartney, “John had a semi-acoustic Gibson guitar. It had a pick-up on it so it could be amplified… We were just about to walk away to listen to a take when John leaned his guitar against the amp. I can still see him doing it… it went, ‘Nnnnnnwahhhhh!” And we went, ‘What’s that? Voodoo!’ ‘No, it’s feedback.’ Wow, it’s a great sound!’ George Martin was there so we said, ‘Can we have that on the record?’ ‘Well, I suppose we could, we could edit it on the front.’ It was a found object, an accident caused by leaning the guitar against the amp.”
Found at YouTube from HDBeatles.