The efficiency of those pro 82+ PSU’s are amazing. I want one lol, they hit 90% in the reviews that i’ve seen. As for the clicking, well there isn’t much inside a PSU to click when inverted, you should be fine.
Maybe its a safety switch so when you PC crashes and possibly flips over, the power to the PSU is cut to prevent your system from igniting.
Since opening the PSU probably voids the warranty, you can email the company and see what they say.