If your drives are Western Digital, you can download the DataLifeguard Diagnostics and DataLifeguard Tools software from the WDC website.
When extracted, the software will create a bootable DOS disk (Floppy or CD).
Boot from the newly created disk and run the full version of the test for each suspect drive.
The software will give you a report with error codes and an explanation of each error that it finds. It will also fix any errors if possible.
Keep a copy of the report, so that you can use it if you contact WDC about warranty replacement of your drives.
If your drives are still within the warranty period, and their Diagnostic software shows that warranty replacement is called for, WDC will usually replace them without question.
Good Luck,
CptA