I got a 92 Mustang with an alluminum driveshaft. It is an auto trans. When I accelerate slowly in 1st gear, i hear a whine comming from the rear. As soon as it shifts into second, it disappears. But then I have a much quieter whine that sounds like a humming, but no vibration is felt. When I slow down and allow the trans to downshift the driveshaft jerks a little and makes the car jerk as well. Then rear is a 3.27 posi and it is stock. What could it be?? The drive shaft does have some small dents and suck on it. Nothing huge though.
