From Nookipedia, the Animal Crossing wiki
K.K. Dirge is a K.K. Slider song. The song is extremely slow, dark, and eerie - the word dirge means a song of lament and sadness. It is unmelodious and discordant. Its instruments are unknown, but there is a constant string bass line, a piano dissonance at one point, and then a crash of cacophony at another. Lucky, Pate, Gaston, Coco, Roscoe and Grizzly play it in their houses.
If you really listen it sounds a little like the Boo's Mansions in the Mario seires.