every once in awhile i randomly get this output in the "MinecraftDev" console:

Client> SoundSystem shutting down...
Client> Error in class 'SoundSystem'
Client> Command thread did not die!
Client> Ignoring errors... continuing clean-up.
Client> Error in class 'SoundSystem'
Client> Problem during Library.cleanup()!
Client> Ignoring errors... continuing clean-up.
Client> Author: Paul Lamb, www.paulscode.com

and this:

Client> Error in class 'CodecJOrbis'
Client> Unable to acquire inputstream in method 'initialize'.
Client> ERROR MESSAGE:
Client> minecraft:sound/piano2.ogg
Client> STACK TRACE:
Client> bhp.a(SourceFile:37)
Client> bhx.a(SourceFile:34)
Client> bhx.a(SourceFile:27)
Client> biz.getInputStream(SourceFile:65)
Client> paulscode.sound.codecs.CodecJOrbis.initialize(CodecJOrbis.java:281)
Client> paulscode.sound.libraries.SourceLWJGLOpenAL.play(SourceLWJGLOpenAL.java:616)
Client> paulscode.sound.Library.play(Library.java:706)
Client> paulscode.sound.libraries.LibraryLWJGLOpenAL.quickPlay(LibraryLWJGLOpenAL.java:795)
Client> paulscode.sound.SoundSystem.CommandQuickPlay(SoundSystem.java:1866)
Client> paulscode.sound.SoundSystem.CommandQueue(SoundSystem.java:2438)
Client> paulscode.sound.CommandThread.run(CommandThread.java:121)
Client> Error in class 'SourceLWJGL OpenAL'
Client> Audio Format null in method 'play'
Client> Exception in thread "Thread-6" java.lang.NullPointerException
Client> at com.jcraft.jorbis.Block.<init>(Block.java:55)
Client> at paulscode.sound.codecs.CodecJOrbis.initialize(CodecJOrbis.java:252)
Client> at paulscode.sound.libraries.SourceLWJGLOpenAL.play(SourceLWJGLOpenAL.java:616)
Client> at paulscode.sound.Library.play(Library.java:706)
Client> at paulscode.sound.Library.play(Library.java:675)
Client> at paulscode.sound.SoundSystem.CommandPlay(SoundSystem.java:2076)
Client> at paulscode.sound.SoundSystem.CommandQueue(SoundSystem.java:2599)
Client> at paulscode.sound.CommandThread.run(CommandThread.java:121)

it works again if i restart the game. there's nothing specific that i'm doing when it happens. i've noticed it go silent while i'm breaking a dirt block, while walking around and having a chicken's cluck seem to cut out in the middle, etc.