The game does not have stamina but if you are running you are easier to detect and vent aliens detect you MUCH faster than if you are walking over their turf.

You can not outrun aliens.

Also, marines can not shoot on the run but they can if they walk.

Afaik running does not create"noise" but stuff like grenades, shooting, and blowing up stuff with C4 creates noise.

If there is noise most aliens and sometimes human enemies will investigate the noise source.

During the noise investigation they are MUCH more likely to detect you if you are near the noise source it is basically instant detection on nightmare.

You can also shoot a grenade somewhere just for noise creation.

Flame throwers, plasma beams skill, and silenced sniper rifles do not create noise.

I do not know if land mine explosion creates"noise"(game mechanics-wise).

I barely used the strong flashlight not sure if enemies could detect it or not.
It is primarily used to highlight loot but I always check the map too as it reveals everything.