It's called Unchained Melody, recorded by The Righteous Brothers. It is the same song used in Ghost, starring Patrick Swayze and Demi Moore- the film Naked Gun is parodying in this scene.
Unchained melody was playing at that time. In naked gun 2 scene This song is also used in other movies. Nd scenes . This is awesome mind blowing melody. I also have Heard it so many times.