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Have you over clocked your card?
It could be you power supply, do you have another one to try?
Have both issues only occurred in Wildstar? Might be a game issue (it is new still right?). Either way I wouldn't write off the GPU just yet, maybe try some benchmarks like Valley/Heaven to stress it out and see how it acts.
how much cpu/vtt are you using? freezes and sound loop usually point to pc memory or gpu memory secondly