Some sounds disappear e.g. You can hear sheep and cows but no movement or block-hit-sound

In SSP and SMP some sounds do not play.
For example you can hear cows trample and moo and also hear floating water, but
no movement sounds an block hit sounds. (Block breaking sounds are allright).
After some time the sounds return. A few minutes later they are gone again.
When you change the music and sound volume the bug reappers.