I've recently started hearing up an odd 'motor boat' type noise with my NEC3500 during DVD (pressed) playback. Seems to afflict all DVDs. CD audio, albiet on a different drive (a Lite-On) seems fine. Haven't noticed any recent burning or ripping problems; just the odd noise. I have many audio programs on my computer and none of them exhibit this problem except DVD playback.
By the way, I use ATI's DVD playback software (came with my ATI All-In-Wonder); and, I have not installed any new software (or hardware) lately.
Could my NEC drive be doing this???