After a short period of silence he says that it was a blast coming from the dial shaped disc of the high gain antenna on the rover (vehicle). More objects start flying over and again we hear genuine excitement. Then the astronaut realizes that he had said something he should not have said in front of the cameras and NASA. He reluctantly accepts the vague explanation. He is really annoyed and you hear sarcasm and disbelief in the undertone of his voice.
NASA tries to save this unpleasant situation and intervenes as CAPCOM confirms that it was a blast from the antenna and that it happened before.
According to the astronaut who clearly is in charge, this blast from the antenna is just "routine".
This is an interesting video. Styrofoam blowing up? This has happened before? When this really would be the case, would they not have taken countermeasures?
Space programs are planned with utmost precision and they do not take any risks with equipment and astronauts.
So what do you think after having seen the footage? Was it a blast from the antenna? Exploding styrofoam? An Comet/asteroid? Or is someone not telling us the truth and these two astronauts had a couple "visitors" passing by.
You probably need to watch the video a couple times as it happens very fast! Unknown object at 0.38 and 0.39 seconds in the video.
Original video EVA-1 Close-out Journal Text: 123:27:46 http://www.hq.nasa.gov/alsj/a17/