First of all, take a look here;
Link and look for a topic on Wav Looping, and then your find out what to do.
Else if you want it to be repeated when you want, but not always repeated, IE: activate for a certain when you want it to.
Conditions:
Set Switch Whatever
(Death Count for Unused Unit Owned By Player Whatever =1)
Actions:
Play Wav
Clear Switch Whatever
(Set Death Count for Unused Unit Owned By Player Whatever to 0)
Preserve Trigger
That will run each time another Trigger sets it up.