That specific G major loop represents the last moment before the ocean got scary, before Nemo got lost, before Marlin had to face the sharks. It is the sound of innocence, preserved in magnetic tape and encoded in a major key.
: Ironically, while "G Major" refers to the musical key, the movie itself is rated
Start with the classic blue Disney/Pixar logo, then transition into the inverted "G Major" effect right as the distorted audio hits.
However, the true highlight—and the reason people search for these videos—is the dialogue. Finding Nemo is a dialogue-heavy film, full of distinct vocal performances by Albert Brooks (Marlin) and Ellen DeGeneres (Dory).