Your car is rear wheel drive with a solid axle rear. Is the noise coming from the differential? Check the oil level, or perhaps change the oil. Could it be a rear wheel bearing. Jack up the car, put two jack stands under the rear axle tubes and drop down the car, start up the car and drive it in gear see if you can duplicate the noise or locate which side of the car the noise comes from. Sounds like a wheel bearing or bad differential bearing.