You can download a zip file containing null.mp3 replacements for the victory music

Extract the sound_win.zip [2] to the route dod directory so it looks like this.
C:\ProgramFiles\Valve\Steam\SteamApps\youremail\dayofdefeat source\dod\sound\ambient\*.mp3

**Please note that this is fine for pubs but may not be legal for League play**
Check with their rules if you are competing. Easy enough to simply rename the sound directory before a league match at this point. The custom maps havent added any map specific sounds.