I think they all calll them self adjusting anymore, but if it's anything like the ones I've owned, it is self adjusting only to a point. What I mean is they have a spring that tensions the belt within a specific range of motion, but once a belt gets too worn and loose, the tensioner itself needs to be adjusted. My manual say my spring should be a certain length to be provide correct tension on the drive belt for the deck. If it is out of spec, it explains how to adjust that spring to get it back in spec and tension the belt correctly.
Forgot to add that I just read your thread and the one reply you got about hitting something with your V-ride. I'd do just as that guy said and change the belt. If it has a crack, it is getting too worn to be realible and your belt tensioner may not be tensioning it correctly due to the wear and crack in the belt. Also like he said, you prolly just noticed it after the "big bang" because you were actually paying attention to potential troubles after that.