Vibrations (1968)

Barbara, a frustrated writer who is also sexually frustrated, seeks to recharge her life by moving into a Manhattan apartment, where she earns money typing up manuscripts for other writers. Next door, a sexy young lady plays a variety of erotic games revolving around her hypnotically humming vibrator. When Julie, Barbara's hot-to-trot sister shows up, she reluctantly allows her to stay, even though memories of incestuous girlhood explorations between them cause her obvious distress.