Music sound dips in and out while playing in Itunes, but songs advance through playlist.

Does anyone know how to fix the issue with the music going in and out while playing in Itunes? It happened before, I reinstalled it and it played correctly for a month. Yesterday it started again dipping in and out. I have tried everything that I know how to do so I am in desperate need of help. It makes for an awful listening experience. It is sporadic in a sense but happens continuous in the sense that it happens multiple times within each song as it proceeds to play through the playlist.