Moved your thread, since its in the wrong forum
That is a seriously weird problem. The playback itself is affected??...
What software are you using to play the DVD's?
Does it by any chance have a setting, within Settings/Playback (or similar) to play at a certain speed? This might be dependant on the drive. Definietly worth checking that!
Is it skipping? So not playing 2x, but seeming like it is, by skipping a multitude of frames?
If so, try another DVD, and see if this works.
I'm hoping its simply a setting in your DVD software you've accidently hit, thats activated the setting on one drive, and not the other.