A single crack comes from a short lightening bolt if you are near the bolt. A multiple crack might be heard if there are some tall buildings or cliffs nearby. I've heard the crack sound from about 50-75 yards away, a short bolt hitting a telephone pole. It was a very short sharp loud crack.

Out here were I live in the West now, we have some 60-ft tall cliffs about a half mile away. We can see thunder storm clouds coming toward us. They are usually fairly small, but they are filled with lightening bolts. The further they are away, the more "booms" we hear, and echoes too. The closer the lightening is, and if it comes pretty much straight down from a cloud that is not very high, we here a sharp crack, with maybe some echo from the cliffs.

I haven't seen the movie. Were they trying to say there were regular distant lightening bolts that had no sound? I don't think that's possible.