Several years ago on the program On The Media, I heard a story that remains one of my favorite pieces of radio. The (sadly) late reporter John Solomon did an excellent story on the editing techniques that public radio journalists use to make our stories sound so clean and polished -- things like trimming source quotes (for clarity, mind you, not content!)
It's a fascinating and very funny look at what goes on behind the scenes, and it's an aspect of our work that a lot of listeners don't know about.
I don't think there's anything unethical in what Solomon describes, but it certainly highlights some of the ways a radio journalist lacking in scruples could manipulate a piece of audio. While it's harder (though not impossible) for broadcast media to engage in the kind of fakery that occasionally gets uncovered on the print side, I think it's in everyone's interest to know exactly how the radio stories you enjoy get put together.
