s_khz
The client includes "sound interpolation" which allows it to play sounds at higher frequencies, than the default 11025 Hz with perfect quality. In addition to "s_khz" also "s_bits" will have an influence on interpolation quality. This variable allows you to choose the frequency you want to interpolate the sounds to. You will quickly discover, that the shaft sound is different at increased sampling rate. That's because shaft sounds were recorded at 22050 kHz, so probably that's how they should sound from the beginning. If you don't like it, you can always convert them to 11025.
11
11khz sound (default)
22
22khz sound
44
44khz sound
48
48khz sound (Linux only)
It must be set from the commandline (ex: ezquake +set s_khz 44)

Also you can change it 'on fly' - just do s_restart after you change s_khz