Here's how to do it, step by step:
Firstly create a script (.sqs) file within the mission folder.
To do this, create a new txt. file and change the extension to .sqs
next, open the .sqs file, (N.B. Make sure you uncheck the box which reads 'always use this program to open this file' if it's ticked.
In the script file write the following:
#Loop
playMusic "track1"
~10
GoTo "Loop"
(Explanations (The following isn't part of the script))
#Loop (where the loop begins)
playMusic "track1" (where you choose the track, "track2", "track5", etc.)
~10 (amount of seconds that the track runs for)
GoTo "Loop" (code that tells the script to back to #Loop)
I hope this helps. Go to the editors depot and read some tutorials.