In what way is the motif of sound used to inspire feelings of horror and suspense in the reader at the end of Chapter 16?

At the end of Chapter 16 when the narrator, R, and the old man are winding up their celebration of the old man's birthday in R's hidden room, the doorbell suddenly rings. The use of the sound of the doorbell is used her in a similar fashion to its use much earlier in the novel, but at this point the stakes are much higher due to R's presence in the narrator's home.