T M

I'm having the same problem on GNU/Linux (Ubuntu 12.04). Sound worked before and now it doesn't:

java version "1.7.0_25"
OpenJDK Runtime Environment (IcedTea 2.3.10) (7u25-2.3.10-1ubuntu0.12.04.2)
OpenJDK Server VM (build 23.7-b01, mixed mode)

The sound is working on another computer (Ubuntu 13.04):

java version "1.7.0_25"
OpenJDK Runtime Environment (IcedTea 2.3.10) (7u25-2.3.10-1ubuntu0.13.04.2)
OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode)

Here is a sample of some of the error messages I'm receiving:

[09:55:52] [Client thread/INFO]: LWJGL Version: 2.9.0
[09:55:53] [Client thread/INFO]: Reloading ResourceManager: Default
[09:55:53] [Sound Library Loader/INFO]: Sound engine started
[09:55:54] [Client thread/INFO]: Created: 512x256 textures/blocks-atlas
[09:55:54] [Client thread/INFO]: Created: 256x256 textures/items-atlas
[09:55:57] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:gui.button.press
[09:56:00] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:music.menu
[09:56:07] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:gui.button.press
[09:56:11] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:gui.button.press
[09:56:12] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:music.menu
[09:56:39] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:minecart.base