Blow Out

While in post-production on a low-budget exploitation film, Philadelphia sound technician Jack Terry (Travolta) is told by his producer that he needs a more realistic sounding scream and better wind effects. After leaving the studio to record potential sound effects at a local park, he sees a car careen off the road and plunge into a nearby creek. Jack dives into the water to help, discovering a dead man and a young woman, still alive, trapped inside the submerged car. He pulls her to safety and accompanies her to a local hospital. Jack learns that the driver of the car was the governor (and a presidential hopeful); the girl was an escort named Sally (Allen). Associates of the governor attempt to whitewash the incident by concealing that Sally was in the car, and they convince Jack to smuggle Sally out of the hospital with him.
Jack listens to the audio tape he recorded of the accident, wherein he distinctly hears a gunshot just before the blow out that caused the accident. He sees a television report that, seemingly by coincidence, Manny Karp (Franz) was also in the park that night and filmed the accident with a motion picture camera. When Karp sells stills from his film to a local tabloid, Jack splices them together into a crude movie and syncs them with the audio he recorded, becoming even more suspicious that the accident was actually an assassination. Unknown to Jack, Sally and Karp were both co-conspirators in a larger plot against the governor. The gunman, Burke (Lithgow), intended that Sally also die in the crash. He begins murdering local women bearing a resemblance to Sally, whose deaths are attributed to a serial killer, "the Liberty Bell Strangler". Jack draws Sally into his own private investigation of the incident. She steals Karp's film of the car accident, which, when synced to Jack's audio, clearly reveals the gunshot that anticipated the blow out. Nevertheless, nobody believes Jack's story, and every move he makes is immediately silenced by a seemingly widespread conspiracy.
Finally, Jack attempts to gather irrefutable proof of the assassination attempt, wiring Sally with a hidden microphone and sending her off to meet a purported media contact. Shadowing her from a distance, he is alarmed to see that his supposed contact is Burke, not the reporter. Sally is the last loose end for Burke to eliminate, and her death will be attributed to the "Strangler". Immediately realizing that she is in danger, Jack attempts to warn her, but Sally and Burke slip out of range and into the Liberty Day parade. Jack makes a mad dash across Philadelphia, attempting to head them off and rescue Sally. He crashes his Jeep, however, and is knocked out. By the time Jack awakens, Burke has taken Sally to a rooftop where he attacks her. Still listening in on his earpiece, Jack spots them. He hears Sally screaming as he rushes to save her, but he is too late. He arrives just after Burke has strangled her to death and is marking her body with the Strangler's signature bell pattern. Jack takes Burke by surprise, overpowers him, and manages to stab him to death with his own weapon. Jack, devastated and on his knees, then takes Sally's lifeless body in his arms.
Ironically, Burke's death ties up the last loose end and the cover-up is a success. Jack begins listening to the recording of Sally's voice over and over again, becoming obsessed with it. In the last scene, Jack is back in the editing room and it is shown that he used Sally's death scream in the exploitation film. The producer is ecstatic that he found a perfect scream and plays it multiple times, forcing Jack to cover his ears.

Question: what does Jack listen to distinctly in the audio tape ?
Answer: Jack listens to a gun shot distinctly in the audio tape.