The "Lord of the Rings" filmmaker Peter Jackson uncovered the Fab Four pair's ruse while researching his new three-part "The Beatles: Get Back" docu-series, which debuted on Disney+ last week (ends26Nov21), using footage originally captured by Michael Lindsay-Hogg for his 1970 film.
Jackson was able to use technology to turn down the volume on the guitarists' instruments to make their chatter audible.
"It's a little bit naughty," Jackson told The Independent. "We came to realise that John and George in particular were very aware that their private conversations were being taped."
"Michael (Lindsay-Hogg) hid microphones everywhere to try and capture candid conversations, but what John and George used to do was turn their amps up loud and strum their guitars - not playing anything - so that's all Michael's microphones were recording. They were in this sort of running battle."
The "Let It Be" film and Jackson's revamp chronicles the Beatles' efforts to write, record and rehearse new songs at Twickenham Studios in London ahead of a planned rooftop concert, which was to be the group's last.
Members of the group and fans have often criticised Lindsay-Hogg's film for being a miserable depiction of the demise of the Fab Four, whereas surviving members of the group, Ringo Starr and Paul McCartney, are raving about the new docu-series.
"Paul actually said to me when he saw it, 'That's a very accurate portrait of how we were then'," Jackson said. "I get the feeling there's no concern about their image anymore."
"I tried to portray them as I was seeing them (and) the band themselves didn't want a whitewash, they didn't want it sanitised."