In the first paragraph, the narrator repeats the words "very," "how," and "heard." His nervous repetitions undercut the idea that he is, as he claims, "calm." He comes across as overwrought and on edge.
In the second paragraph, the narrator repeats the phrase "there were none" and states the word "eye" over and over. In the third paragraph, he repeats the word "steadily, steadily." As he opens the door to the old man's room, he says " stealthily, stealthily." As he is about to kill the old man, he repeats the word "louder." After he is done disposing of the body, he repeats the word "ha!" In the second to last paragraph, he repeats the words "sound' and "noise" and ends with following repetition—"louder! louder! louder! louder!"
Four spots where he repeats a word consecutively are: "steadily, steadily"; "stealthily, stealthily"; "ha! ha!"; and "louder! louder! louder! louder!"