Little Update:
I am guessing it ''could" be a common thing, after a week of messing around and I checked whatever I can to without pull off headliner or taking things apart (don't think it's moonroof).

So I ended up getting bunch of sound soundproofing foam from Amazon and just shoved it into inner spaces after taking off the rear door weather strip. Even into spaces around curtain airbag, in case of accident, I don't think the foams will interfere with deployment.

This definitely defused the sound, whether it was traveling from somewhere or directly, the tick noise is still there faintly, but not enough to bother me anymore.

My overall guess is it's from attached points of curtain airbags. There are number of them attached to the metal body. Something is rubbing and flexing during the vibration of driving.