That said, I'd enjoy knowing how to do this myself. I think I could figure out the XML part, but killing the noise is the more important thing to me.
Actually, it looks like someone has already created a karma version. I haven't tired it out yet, but here you go:
http://www.newvegasnexus.com/downloads/file.php?id=34784
When you look in the file you'll see there are silent sound files. Whenever you want a sound to go away in the game, you have to replace the appropriate sound file with a silent version. To find out the names of the sound files, and folder structure, you have to use something like BSA Commander that allows you to extract all the sounds out of the archives.