All sound files are Public Domain (CC0).

They can  be found at this locations:

http://opengameart.org/content/rpg-sound-pack
http://opengameart.org/content/gui-sound-effects
http://opengameart.org/content/5-break-crunch-impacts
http://opengameart.org/content/platformer-sounds-terminal-interaction-door-shots-bang-and-footsteps
http://opengameart.org/content/metal-interactions
http://opengameart.org/content/8-wet-squish-slurp-impacts
http://opengameart.org/content/level-up-power-up-coin-get-13-sounds
http://http://opengameart.org/content/50-rpg-sound-effects