Are you sure this is actually used in game? We have a lot of sounds not used ingame and I believe that the common dirt sounds will be used instead of the mud sounds you posted, but I am not 100% sure.
Regarding footstep sounds, the footstep sound associated with texture: textures/darkmod/nature/dirt/dry_earth_muddy is a wet mud sound, not a dry sound as you'd expect.
I have no idea how to go about switching it for the dry one, so I am using a nodraw sound solid patch to "overwrite" it in map.
You can type s_drawsounds 1 in the console to see what shader is being used.
Edited by SeriousToni, 12 March 2016 - 07:26 AM.