|I assume you have been testing the drive with Hitachi's Drive Fitness Test (DFT), though you haven't mentioned it, so I'm guessing you have.|
Hitachi's official explanation:
Hitachi disposition code 0x72
This indicates that your hard disk drive has problems reading one or more of its sectors. In most of these cases the drive can heal itself of these errors. To do this first back-up all your data from the problem drive ( if possible ) then run DFT again and select either the Erase Disk or Sector Repair option which is under the "Utility" heading.
If you already have a backup of the data on the hard disk or the data isn’t important you can opt to run Erase Disk or Sector Repair from the "Test Result" screen. Once the selected operation has completed you can then run one of the test options Quick or Advance to confirm that the drive has been healed.
The test result code should then be displayed as 0x00 (drive now healed and OK).
If the test returns another code then you should check with your drive/system vendor if the drive can be returned for warranty replacement (depending on when it was purchased).