The Champion Blue victory music muting glitch or silent Indigo Plateau glitch is a glitch in Pokémon Red, Blue, and Yellow.
If a Pokémon evolves or has its evolution canceled just after the battle with Champion Blue, then the music will be muted (instead of the victory music continuing to play) until the slowed down version of the Viridian City music plays.
This applies to both the intended Blue battle, and also Champion Blue encountered through the old man trick (via a '/' as the 3rd, 5th, 7th, 9th or 11th character) or Ditto trick (via a Special stat of 243).
If Blue was encountered through the old man trick or Ditto trick, then the music will be muted until:
Entering a new route or town via map connection. Flying, teleporting, using an Escape Rope, or digging away, Entering a battle and winning or losing (causes the Champion Blue music sticking tricks)
Entering a new warp not through a connection causes the muted music (or otherwise the previous music) to stay.
Bring a preferably low leveled Pokémon that can evolve, such as a Caterpie (evolves into Metapod at level 7) into the Elite Four. Have the Pokémon that can evolve level up to cause the evolution screen after the battle with Blue, and win. Either allow the evolution of cancel it.
Champion Blue music sticking tricks
Youtube video by ChickasaurusGL. This glitch listed on Pokeglitch.