Where does the rapping come from the second time?

In the sixth stanza of "The Raven," the speaker observes that he again hears a rapping. In the first stanza he heard it as a tapping at his chamber door, but the second time the sound is concentrated at his "window lattice." A latticed window features strips of metal that function to hold small pieces of glass in place, as in a multi-paned or stained glass window. The tapping or rapping is louder this time, either because it is closer to the speaker or because the entity seeking entry is more insistent than the first time. The speaker goes to the window and opens the shutter; and, into his chamber steps a "stately Raven," a large black bird that ranges over the majority of the world's northern hemisphere.

The first time the narrator hears the rapping at the door, he answers it to find that there is no one there. He whispers his dead lover's name, Lenore, hears it echo back to him, and then he turns back into his room, feeling upset anew. He then hears "a tapping somewhat louder than before" (line 32). He hears that something is tapping at his window, and he assumes it is the result of the wind blowing and nothing more. He opens up the shutters, and a strange raven steps into the room via the now open window. The raven does not seem at all afraid or wary of the narrator; in fact, the narrator describes the bird as acting as though it were a lord or lady. The raven perches on a bust of Athena that the speaker has standing above the door to the room.