This invention relates to an improved structure for a rack drive assembly adapted for use in a vehicle electric power steering assembly. The electric power steering assembly includes a steering member (32), a ball nut assembly (70), a bearing assembly (80) and an electric motor (60). The steering member (32) is disposed in a rack housing (30) and includes a rack portion (34) operatively connected to a vehicle steering wheel (12) and a screw portion (40) having an external thread convolution (42). The ball nut assembly (70) is operatively connected to the screw portion (40) of the rack portion (34) of the steering member (32) for effecting axial movement of the steering member (32) upon rotation of the vehicle steering wheel (12). The ball nut assembly (70) includes a rotor shaft (76) and a ball nut (72) fixed to the shaft (76) for rotation therewith. The ball nut (72) includes an outer surface (96) and the rotor shaft (76) includes an inner surface (114). The bearing assembly (80) is carried by the rotor shaft (76) for rotatably supporting the ball nut assembly (70) relative to the steering member (32). The electric motor (60) is operatively coupled to the rotor shaft (76) via a pulley assembly (82). The power steering assembly further includes an insulator (74) disposed between at least a portion of the outer surface (96) of the ball nut (72) and the inner surface (114) of the rotor shaft (76). The insulator (74) isolates the ball nut (72) from at least one of the pulley assembly (82) and the bearing assembly (80) to thereby reduce the noise in the ball nut assembly (70).