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.
If it's the same contactor sound your PC makes when booting up and shutting down, it's most likely your PSU. What is the model of your PSU? How old is it?
Oh it definitely is still in warranty, it has 10 years total warranty.
Ordered a 750w model to see if it stops the shutdowns, after that I either return it or trade it from warranty.