So I kinda figure it's either the PSU or one of my hard drives, but what the issue is is that me PC first makes a click sound (as if I physically shut it down), then restarts some time after.

When it restarts it makes a bit noisier click sound, same as the power button switching does.

I have verified it's not ghosts or little green men. I can't say for certain about Martians.

It's just weird. I'll be unplugging both HDD's today to see if it goes away. Then one-by-one plug things in/out.