Sources for the various sound files:

[silent.ogg]
Generated 2 secs of silence - dd if=/dev/zero of=silence.pcm bs=176400 count=2 ; oggenc -r silence.pcm
Generated by Neil Muller, Aug 2010
Not copyrightable.

[squeak.ogg]
URL: http://www.archive.org/download/Berklee44v6/Berklee44v6.zip
Source: http://www.archive.org/details/Berklee44v6
License: http://creativecommons.org/licenses/by/3.0/
Credit: Sound samples from Berklee recorded for Richard Boulanger for use in the One Laptop per Child music library. See http://wiki.laptop.org/go/Sound_samples for details.
squeak.ogg wavfile: rubber_toy_short1.wav

[crash.ogg]
URL: http://www.archive.org/download/Berklee44v12/Berklee44v12.zip
Source: http://www.archive.org/details/Berklee44v12
License: http://creativecommons.org/licenses/by/3.0/
Credit: Sound samples from Berklee recorded for Richard Boulanger for use in the One Laptop per Child music library. See http://wiki.laptop.org/go/Sound_samples for details.
crash.off wavfile: small_wood_crash1.wav
Truncated and re-encoded via: head -c 47596 Berklee44v12/small_wood_crash1.wav | oggenc -o crash.ogg -