Read the trailer's quiet track.

A deck's: The quiet track sends every render of the deck that has no spoken line a voice track with nobody speaking in it (silence, or a soft room tone), the way a spoken render is sent the cast's lines, to test whether quiet faces keep their lips closed when the render hears a track. It is off by default and free, and it changes only the takes rendered after it is set: each take records the track it was sent, and a take already made keeps what it had. A render with a spoken line, and a chapter that keeps its own sound (bells, singers, a crowd), never gets one. A chapter that played its render's own room tone plays the track (silence, or the hush) instead. A trailer's: The quiet track sends every render of the trailer that has no spoken line a voice track with nobody speaking in it (silence, or a soft room tone), the way a spoken render is sent the cast's lines, to test whether quiet faces keep their lips closed when the render hears a track. It is off by default and free, and it changes only the takes rendered after it is set: each take records the track it was sent, and a take already made keeps what it had. A render with a spoken line never gets one. A beat that played its render's own room tone plays the track (silence, or the hush) instead.