My crossfired 5830's have the same issue as your 6990. One is pretty constant and the other is all over the place. It doesn't matter which is in the 1st PCIe slot it still happens. Annoying so I try not to look lol Another anomaly is intermittently getting "connection problems" with that second adapter. I'll get home from work to find out it hasn't been running for hours. I was hoping the switch to some form of linux would fix this?