MuteLocal.cs
Available at http://www.crushedfrogs.org/MuteLocal/. Versions for VikingPack, UltraLite, Stripped and Presto can be found on the site. 
Info
Brought to you by your beloved ced & ruWank. Thanks to haze, we made him work on something which ended up being useless (for the script, that is) :}
The script mutes the local sounds. It's quite simple, we set the $pref::playVoices variable to false, and then to true when we receive a message with a sound attached (it's set back to false immediately so you will still here the messages in the chathud -- but not the local ones) :) 

"Bugs"
It will also mute the sounds attached to the waypoints command, because those ones do not go through the onClientMessage function so we don't catch them. 
You might hear, rarely, a local sound. It will happen if someone around you makes a taunt while at the exact same time you get a message with a sound in the chathud (tho the sound of the message in the hud should cover the local taunt noise :]) 

Install
To install, place this file in your config directory and add the following line at the end of your autoexec.cs: exec("MuteLocal.cs"); 
You can use F8 to enable or disable the script ingame 

If you are using the MuteLocal.cs stand alone version, you will need some editing, check the comments in the file 

Download
Stand alone version (MuteLocal.cs) 
VikingPack version (MuteLocal_VikingPack.cs) 
UltraLite 2.1 version (MuteLocal_UltraLite21.cs) 
UltraLite 2.0 version (MuteLocal_UltraLite20.cs) 
Stripped/Presto version (MuteLocal_Stripped_Presto.cs) 



QuietGame.cs users
If you are using QuietGame AND you intend to use MuteLocal, you'll only need the MuteLocal.cs stand alone version and to replace your QuietGame.cs version by one of those : 
Stand alone version (QuietGame) 
VikingPack version (QuietGame_VikingPack.cs) 
UltraLite 2.1 version (QuietGame_UltraLite21.cs) 
UltraLite 2.0 version (QuietGame_UltraLite20.cs) 
Stripped/Presto version (QuietGame_Stripped_Presto.cs) 
All you should need is add both files in your autoexec.cs 