if I’m about to fall asleep and I happen to hear a loud noise nearby,

https://vester.si/bodily-oddities/oddities/hypnagogic-halluc...

I also see a flash of light with my closed eyelids.

You might want to talk to a optician about that. It can be a sign of issues with your retina.

I see flashes in a dark room when I wake up, because I have PVDs (posterior vitreous detachment) in both eyes.

Edit: I just re-read your post. If they both happen together, I think it is something different.