What are your miner command line settings?
Also, is your power supply large enough?
If possible, try downclocking the memory to 300 MHz, that might lift some strain on the PSU.
miner settings -v -w128
How to downcloack the memory in ubuntu 1104?
Looks like your cards are highly restricted in over/underclocking range, aticonfig won't do. AMDOverdriveCtrl, on the other hand, might just do that.
Get it here:
http://sourceforge.net/projects/amdovdrvctrl/files/C%2B%2B%20sources/AMDOverdriveCtrl.1.2.0.tar.bz2/downloadIf you don't run headless, just start it and adjust the values. If you do, post, and I'll be back
