Chris,
I wish I knew more about external RAID devices for you.
It may be a problem with the LaCie enclosure since the drives seem to work fine when placed inside the case.
I'm not sure if this is the model you have, but you should check at LaCie for any driver, firmware, or software updates that may help. If not, you may also contact the support at LaCie to see what they say or if anyone else has experineced this to.
LaCie - 2big Triple (2-disk RAID) - FireWire 800, FireWire 400 & Hi-Speed USB 2.0
Hope this helps,
Shawn