The whispering is symbolic of the family's financial problems. The phrase, "There must be more money," is the family's constant worry, but it is never spoken about openly. Thus, Paul senses this anxiety as "whispering" and decides he must do something about it. Once he is successful and gives his mother 5,000 pounds, the voices go mad because the mother can never be satisfied with what she has. As soon as she has spent the money the voices begin screaming, "There must be more money. . .more than ever! More than ever!" It seems both his mother and the voices will never be happy with the money they have and will always want more.