This has happened four or five more times since I posted the first note. If I pull the unit out of the sled and let it sit for a minute or two, then plug it back in, it works ok, and can play the whole track that it hung up on previously.

I have brought it in to work with me and left it plugged into the A/C adapter and playing tracks all day (8+ hours) and it's run flawlessly the whole time. l also ran "badblocks" against the drive and it showed no problems. But I've got about a 50% chance it'll display "drive active icon with a W" and stop being able to access the drive at some point on my drive in to work or home from work.

Could this be a component going flaky that's only in use when it's plugged into car power? I can hear the drive spin up when it does this and I've pulled out/plugged back into the dock in the car, so it doesn't seem like the drive is flaking out, at least in terms of stop functioning.

It's not disastrous as I can just wait a couple minutes and then plug it back in, but it's certainly annoying.