IF YOU ALREADY KNOW ABOUT THIS FIX, GOOD FOR YOU!
Have you ever encountered a WAV file that doesn't play in-game ? here's how to fix it
Download Wave Editor http://www.wave-editor.com/waveditor.exe oh and its free btw !
Once downloaded Install and open the WAV file that you're gonna fix.
1. once loaded, check if the end of the wav file has a blank wave form, if it does,highlight the blank wave form and delete it.
2. (This is what's causing the problem) go to the beginning of your wave form, check if it has a blank wave form at the start, highlight and delete it ! )
FINALLY don't forget to rename your wav file if its not already renamed to SFXXXX.wav ( replace the XXX to whatever number that you need).
Goodluck !