Whenever the background singing comes up it just sounds like he's whispering to himself as someone would when singing to a song without it playing in the background
I never herad this before i omly heard the one from the tv series thats like “so george and harold make comic books were cool me too but they had a mean old principal that told them what to blah blah blah blah”
This one is from the film adaptation. (This song was written and sung by Weird Al, fitting the series since George and Harold did play Weird Al songs over the school speakers in book one.)