Hey, today i got bored with the music in Summoner's Rift so i searched a bit in the game files to find where the music and sounds are being stored.
C:\Riot Games\League of Legends\RADS\projects\lol_air_client\releases\0.0.0.158\deploy\assets\sounds
This is where all the soundfiles that have to do with the client are stored. You can delete them and paste your own, just make sure they have the same name and extension (.avi).
However i havent been able to locate the in-game sounds and music. Anyone got a clue as to where they can be found?