ok i had a rattling sound for a couple of days, today it had a louder noise and then it completely locked up, i put it in park, shifted into drive and it wouldn't move i increased the throttle and it shuddered forward a foot and locked up again, shifted into neutral and tried to push the car and it wouldn't move, reverse is just the same as drive with a little throttle it moves a bit, ok towed the car home, removed the drive shaft and turned the wheels the posi is fine, what is causing this ?