This is my theory:

The rear of the drive has an array of exposed pins (for settings), which almost stick out a pit. They face the LC's rear case cover, which is plastic but metal clad on the inside side. I think that the pins were conducting electricity via this metal surface, although I'm not sure if they're close enough to do this when the cover is closed. Either way, I put some tape over the contact area, and the problem seems to be fixed.