스륵 and 스르륵 describe the sound of an object sliding or being dragged, usually smoothly without obstruction. The best example is probably the sound of a sliding door. Examples: - 이야기하는 중에 미닫이 문이 스르륵 열렸다. The sliding door opened with a rattle while we were talking. - 호텔 문 앞에 서자 자동문이 스르륵 열렸다. I stepped to the hotel's automatic door and it rattled open. (EDIT: since 스르륵 implies a smooth movement, "dragging" may not be a good description of it.)