Thanks; this did the trick.
For those who don't know Lua, open these two files in a text editor.
Search for: PlaySound
Replace with: --PlaySound
The -- is a Lua comment, equivalent to C++'s // comment-line marker.
This doesn't work for every source code file so it's not a blind recommendation for every add-on. However, this particular code has the PlaySound calls on a separate line each time, so it works perfectly.
These comment markers cause the entire line to become a comment and thus not executed; it's easy to revert in the future if necessary.