I think my wife's computer does this occasionally under Windows 7 with our Western Digital World Book, but unfortunately I don't have an explanation for it, and I think it stopped doing that after I recently updated the firmware.

FAR more annoying to me is that the stupid drive will simply quit during big file transfers. Like, I'll try to move 8GB of files to it, and the transfer will freeze after about 5GB, and be completely unresponsive until I reboot it. I can't tell you how annoying it is, and I've had zero luck with support from Western Digital on this. In fact, in my first call to them, they stated that the drive wasn't compatible with Windows 7. That seems highly unlikely to me.

Anyway, sorry to hijack there. I just needed to vent a little