Could be a few things,
Clocks in overdrive are too high
(Anything I'm missing? This doesn't sound like a power issue)
A few things you could try to identify the issue:
Check your temps, if high clean fans, used compressed air to clean the card.
Lower your clocks slightly in CCC and see if the issue persists.
Try the card in another computer if all else fails.
You can use GPU-z to check temps/ GPU load / clock speeds, to see if the issue occurs at low GPU load as well as high. Good luck.