In the Conclusion of Ethan Frome, who spoke in "the querulous drone" as the narrator entered the house?

In the conclusion of Ethan Frome, the
narrator entered Ethan's house as a courtesy from Ethan considering that he had been the
man's driver for a while. He had known the story of Ethan as the reader learned about
his love fantasy with Mattie, how they plotted a sudden suicide pact, and how the pact
failed, leaving Ethan into a near-paralyzed man.

We know
that, as the narrator approached he heard what he described as a "querulous drone", or a
voice nagging and complaining almost incessantly. We discover that the woman who is
nagging is none other than Mattie herself, who has become now an invalid due to the
accident, and a bitter one at that.  To add to the pain, Zeena is ultimately both Mattie
and Ethan's care taker, making the oppression of Ethan and Mattie not only physical but
moral, psychological and fateful.