DVD Vibration
I have had this experience with several CDs and DVDs on my Sony. After examining the disks that I had a problem with, I decided that the media was not symmetric and that was causing the problem. If it is something that you use regularly, I would copy it to a new disc, but I haven't had a problem with failures or anything. I have heard that some discs will self-destruct, but haven't had first-hand experience with it. I would assume that any disc that is asymmetrical would be more prone to damage though.
HTH