I think you're on to something.  I recall about a month ago Norton chkdsk detected a problem with the MBR of the backup internal disk.  It automatically fixed the MBR, so I didn't give it much thought.

Norton Utilities has a utility specifically for repair of MBR. I didn't run it on the backup internal drive because it gave a scary warning.  "This operation will overwrite existing disk boot loader code with Windows disk boot loader code.This operation could make your system unbootable".

Well, I don't boot from my backup drive.  Is running this repair utility worth a shot?  This MBR is stored on the drive itself, right?  It can only affect my backup drive, right?  Why is there boot code on my backup disk anyway?  I'm confused - sorry if I sound like a newbie.