It wasn't just that they didn't want people hearing Oswald too well. If he spoke, and people just listened, if there was no other sound, then he would have seemed like E.F. Hutton. Do you remember the commercials? "When E. F. Hutton talks, people listen." So, it would have seemed very RESPECTFUL to Oswald if when he began speaking, the audience hushed. So, they added all that noise to deride him, to degrade him, to trash him. Is it possible that they did it right there, live? It's possible, but I doubt it. And that's because: I presume the reporters wanted to hear what Oswald had to say. So, I say they added the sound effects afterwards. Please listen to it again with that in mind.