The only way I know how to loop a sound is by using a script. Have the script play the sound, then delay for a length of time equal to the length of your sound effect, then have the script loop back and play the sound again.
Below is a copy of one of my scripts, generalized for your purposes, that should accomplish what you want.
#loop
; Play the appropriate sound effect.
playSound "MySound"
; Delay for approximately the length of the sound.
~5 ; Change this to the length of your sound effect
goto "loop"
Hope that helps