 Many of the "raindrops" in the final fight between Neo and Smith are  actually single lines of Matrix code, similar to those on displays  seen in the "real world" throughout the trilogy. This subtle effect  was added to imply the Matrix was beginning to destabilize. This  visual trick was easily seen on IMAX and larger movie theaters, but  can be seen on smaller televisions as banded rain that seems to  "jump" like static during close ups of the fight scenes.