1. I would say that the correct answer is pacing. Pacing is the speed of the narrative, affected by different syntactic and stylistic techniques. In this excerpt, we first have a short part of an informative sentence that narrates the story ("then I heard"). Then, the action is stopped and the pacing slowed down - just look at the long, complex-compound sentence that is the center of this excerpt.
2. In my opinion, the correct answer is to build tension. The narrator first introduces a bizarre detail - the vibration of the chains - and then freezes this action in order to indulge in his own psychological issues (enjoying the sound or at least pretending to enjoy it), while he builds tension with the reader who expects to find out what happened next.
