After already having one Superdrive replaced (that crapped out fully) i'm becoming a little bit worried about the second one. I just got done importing some more of my CD collection to Itunes and noticed that the occasional CD will fail to mount. The Superdrive will spin up 3 times before finally spitting the CD back out. This has happened with about 3 CDs I own, all of which are pristine with no scratches or defects. All the affected discs will read fine in my external OWC burner. Is this normal for such a compact slot-drive to not like the occasional disc or is this cause for concern?