I have one of those GPUs and it does not have the same issue. Check the fan for any debris or excessive dust. Also, make sure you don't have any wires touching the GPU that could be vibrating at a certain resonance (causing the sound).
If all else fails, you could RMA the GPU. Sapphire could replace the heatsink/fan or send you a refurbed or even an upgraded GPU, only they can answer that question for you.