Actually, break-ups, atifacts happening in the same spot IS more of a confirmation that it is the SIGNAL. If you are getting the break-ups or problems at different points after replaying, then that is a sure sign of the HDD as that is likely a problem with the READ of the HDD regardless of how well the data was WRITTEN, and if there is a problem with the HDD you WILL get READ problems, guaranteed. My vote for your problem as you have described is more along the lines of what HipKat has suggested.
The HDD is probably writing properly, but the signal is getting botched somewhere along the chain from OTA or Sat origin digital stream to the HDD. Your HDD and error correction are likley trying to READ the corrupted signal/digital stream that was laid down (written) on the HDD as best it can, and these various attempts can result in sometimes different artifacts, but in the same spot because with video/audio, it has to be sent to the output on the fly, as opposed to, say, a Word or Spreadsheet File that the computer can take its sweet time correcting the data for output several seconds or even minutes later.