Got this Client Warning Message when first launch of MC 15w45a:
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:block.brewing_stand.brew
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:block.chorus_flower.death
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:block.chorus_flower.grow
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:enchant.thorns.hit
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.guardian.thorns
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.horse.eat
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.crit
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.knockback
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.parry
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.strong
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.sweep
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.weak
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.rabbit.attack
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shield.block
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.ambient
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.close
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.death
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.open
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker_bullet.hit
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker_bullet.hurt
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.ambient
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.death
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.drink
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.hurt
[07:58:00] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.throw