Problem with MyBook World Edition (Blue Rings) - get alternately flashing rings, but drives say fine

So, about once or twice a day, the drive just starts flashing the alternating rings.  I reboot it, get into the web interface and it always says ‘Drive OK’.  it stays up for a few hours and then the flashing again and the inability to get into the web interface until I reboot it.

I feel like a drive is failing, but with no status on the drives other than ‘OK’ I don’t know which one to replace.  How can I figure out what’s going on here?

There are two 750 GB drives in here in RAID 1.

Try removing one of the drives an test while connected to another enclosure or computer direct