Sound problem

I have a problem with the sound in ET. I always hear some strange noise (prrr... prrr... or like a snake :)) when a sound is played in the game. What do u think the cause is?
The cvars are this:
seta s_channels "2"
seta s_bits "16"
seta s_wavonly "0"
seta s_defaultsound "0"
seta s_mixPreStep "0.02"
seta s_mixahead "0.06"
seta s_khz "44"
seta s_doppler "1"
seta s_separation "0.5"
seta s_musicvolume "0"
seta s_volume "1"
seta s_loadas8bit "1"
seta s_distance "100"
seta s_mindistance "0.000000000001"
seta s_maxdistance "99999999999999"
seta s_polykeep "1000000000"
seta s_polyreflectsize "10000000"
seta s_polysize "10000000"
seta s_bloat "2"