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#11
..to be clear, I meant clicking continuously is a bad sign.
Also as you may have found, you're not the only one experiencing this with WD Green drives:
WD Green drive seems to be slowing whole computer down [Solved] - Western Digital - Storage
Since you are using Caviar Green drives (which you should not be doing for a Linux RAID setup, honestly) and already are at it, make sure to disable the power saving features, especially the IntelliPark feature.
smart - Inexplicably slow Western Digital WD15EARS disk - Server Fault
Western Digital Caviar Green hard drive slow, causes crashes... - HP Support Forum - 792689
+ the comment that it was never meant for use as a primary drive but as mass storage.