You can't do it via triggers, because through triggers you can play only 1 sound at a time.
e.g. if multiple units run, only the first unit (the one which fires the trigger as the first) will play the sound, then no sound will be played until the current sound finishes => it will look horribly in game, random and unrealistic.
The only solution is adding the sound to the model itself - something similar to how missile effects work (the model itself is set up so they play/loop specific sound when in specific animation - e.g. when in "birth" animation, a druid of the talon's missile will play "DruidOfTheTalonMissileLaunch" sound).
The good thing is these sounds are not limited like sounds played via triggers, but the downside is that you have to edit each model and you have to know how to do it.