Blow Out (1981)

Murder has a sound all of its own.

While recording sound effects for a slasher flick, Jack Terry stumbles upon a real-life horror: a car careening off a bridge and into a river. Jack jumps into the water and fishes out Sally from the car, but the other passenger is already dead — a governor intending to run for president. As Jack does some investigating of his tapes, and starts a perilous romance with Sally, he enters a tangled web of conspiracy that might leave him dead.