I'm trying to change the sound Messages makes when sending out an message along with receiving one. 

I've done some tinkering based on info from similiar questions on this site. For example:
[Where are the alert tone audio files located in OS X?](https://apple.stackexchange.com/questions/210072/where-are-the-alert-tone-audio-files-located-in-os-x)

Can someone tell me where files are located for me to make changes. I know the receive sound is called `note.m4r`. But I want to change the sending out "wooooo" sound too.

How can I go about doing this?