Whirlwind sound is automaticaly attached to BladeMaster, meaning that as long as that ability lasts, given sound will be looped. As you can see, in Object Editor, there is no data that determinates sound file (neither in Ability, nor in Buff).
Solution here is: enter the Sound Editor (to the right of trigger editor) and import to your map sound:
Units\Orc\HeroBladeMaster\BladeMasterWhirlwind.wav ->> right click and press 'Use as sound'.
Now you can play that sound via triggers (refer to event - unit casts a spell, and use actions from Sound section).