If I were in your shoes, here's what I would do:
1) Remove the drives, note the make and model.
2) Go the MFR site and download the boot time diagnostic tool. (Seatools for Seagate, etc.)
3) Install the drive in another computer and boot to the diagnostic tool.
4) See if there are bad sectors
What you learn: Drive is good/bad. If drive is bad, replace it and rebuild the array. If drive is good, there is likely a problem with your controller and/or controller driver. Make sure you have the latest driver for your RAID controller/replace the RAID controller.
A bad RAID controller could be indicating that the integrity of an array is good when it may not be.
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