When I am taking off from stop making turns with a slow speed, there is vibration form rear end of my 90' 56sec, it will go away when the car turns straight, it is less noticible if I push the gas pedal a little bit harder. It seems like always happen when the car start moving and turnning. The vibration seems like coming form the differential and is really bothering me. I brought to my mechanic and was not able to duplicate the sympton, any idea?