You can't mod the sound that other people hear, only what YOU hear.
HOWEVER, my mod below is a mach10 superknife, so you can click just once or tap rapidly or hold full auto so it you don't want to be reported, you can just not hold it down auto... That's what I do to avoid being reported when I'm not just playing with noobs.
http://www.mpgh.net/forum/210-combat...d-release.html