One GPU in a rig lowers hash rate - swapping cards swaps low hash rate

[activescott]

I have a rig with four GPUs and three of them are HD 7950. When I upped the clock on the three 7950s, the hash rate went up for two of them and down for one simultaneously. You can see this in the below chart around 12/18 before 4:00am:

https://imgur.com/c0QliZa

I suspect a power issue, but I'm not sure if I should be focused on the PSU power directly connected to the cards or if I should be focused on the PSU power going into the risers. Or both. Can someone save me some trial & error time by pointing me in the right direction if one is more likely to be fruitful?

Thanks for your help!

[activescott]

Is there a better place for me to post questions like this? Just wonder if I’m missing something obvious.