I tried to add my own custom sounds, but it doesn't work. I tried using another resource pack, but theirs worked, and mine's didn't.
MC-48841
Resource Packs not working
Resolved
Invalid
0
(Unassigned)
Unconfirmed
Minecraft 1.7.4, Minecraft 14w05b, Minecraft 14w06b, Minecraft 14w07a
Retrieved
... but that's no bug.