Kbase Article of the Week: Macintosh: External Drive Failures →

Apple Support:

PROBLEM DESCRIPTION: Intermittent and/or solid failure during reading and writing to the external drive.

CAUSE: The pins on the logic board punch holes in the mylar covering on the RFI shield on the back of the logic board. When they penetrate the covering they short to the case.

That sounds like an exciting bug. Here was the “CURE” as Apple put it:

  1. Install the latest revision of RFI shield orderable through Apple Service.
  2. If the problem persists, replace the external drive mechanism.
  3. If the problem still persists, refer to the Level I Technical Procedures.