The first time Oleron hears the spirit making any kind of noise, it seems to be through the rather commonplace sound of a dripping tap, which, the more that Oleron listens to it, appears to resemble a particular phrase of a tune. As Oleron slumps in front of the fire, and presumably begins to go to sleep, he imagines that the drops of the tap are playing a tune, and he has a very clear picture of what the drops look like and how they fall together:
He became conscious of the dripping of the tap again. It had a tinkling gamut of four or five notes, on which it tang irregular changes, and it was foolishly sweet and dulcimer-like. In his mind Oleron could see the gathering of each drop, its little tremble on the lip of the tap, and the tiny percussion of its fall "Plink--plunk," minimised almost to inaudibility. Following the lowest note there seemed to be a brief phrase, irregularly repeated; and presently Oleron found himself waiting for the recurrence of this phrase. It was quite pretty...
Note the onomatopoeia in "plink--plunk," which helps to enact the sound of the falling drops. The "recurrence of this phrase" suggests that something out of the ordinairy is going on. This is an impression that is reinforced the next day when he finds himself humming that very same phrase and it is identified as being part of a song written by the former inhabitant of the house. The tune was called "The Beckoning Fair One," and is a very old tune, Oleron is told by Mrs. Barrett. This of course sets up the story for the ghostly events that transpire.