Like lots of other laptop/notebook owners I have had the optical drive (GSA-T20N) on my laptop (ASUS Z53S) give up on me, so I have purchased an external drive (LG GE20NU11) connected by USB 2 using Win Vista. I have used this for playing/burning ripped disks, both CD and DVD. Sometimes I download a film and burn to disk on the laptop and notice that very occasionally I have trouble playing the disk on the laptop, even though I've just burned it with the same equipment. The DVD has always played in all my other players and I could watch the downloaded file on my laptop, so I didn't fuss too much.
However, the other day I bought a commercial DVD film and found that when I tried to play it on my laptop, it juddered and shook as the heads tried to read the disc. Naturally I tried the disk in every other player I had including my main PC, and none of them had any problems at all.
So I connected my external drive from my laptop, to my PC and again had no problem playing the disk. Back to the laptop and the external drive again started juddering and really struggled to play any part of the disk.
If anyone has experienced something similar or knows how to cure the problem, I'd be over the moon.