The problem of looping background music tracks effectively plagued me for a long time, mainly because of an "exception" to a rule in Blizzard's help file. =P Well, it turns out that it is actually pretty simple. First, you need a computer/neutral/rescuable player that has no other triggers (or rather no other triggers that contain obstruction actions: wait, transmission, center view). Here are the two triggers, assuming Player 1 is the human player who wants to hear the music and Player 2 is the computer/neutral/rescuable player:

Owners:
- Player 1
Conditions:
- 'Music Playing' is cleared.
Actions:
- Set 'Music Playing '.
- Play 'music.wav'.
- Preserve trigger.

Owners:
- Player 2
Conditions:
- 'Music Playing' is set.
Actions:
- Wait for ##### milliseconds.
- Clear 'Music Playing'.
- Preserve trigger.

music.wav is your music track (in wav format, of course), Music Playing is a switch, and ##### is the length of your music track in milliseconds. These two triggers will nearly flawlessly play the music track every cycle of ##### milliseconds without interfering with your other triggers.

DI
April 18, 1999