Before I do that, is there any possibility it could be my PSU?
I wouldn't think so. I'm not sure how a PSU problem would cause a clicking sound from the hard drive. Tho, I've seen poor PSU's cause all kinds of weird issues.
i should add, using my hd5450 out of my htpc or integrated graphics it rocks flawlessly.
With that statement, It's certainly worth testing a better PSU, before sending the motherboard back. The 5450 and integrated graphics certainly use less power.