I've noticed that during certain tracks I'll start hearing the harddisk spin up every couple seconds or so, for the duration of the song. Next song, bam, gone. I was finally able to determine that whenever a track does this the iPod can't show me the track's artwork -- the blow-up that is. The artwork is still viewable in the general screen that shows all the track info.
Anyone else have this occur to them? I'm not even sure the problem is repeatable -- I think if I've listened to a specific track weeks later and not had the problem recur.