All Valiaint experts help me out

Jack the rear tires off the ground and pull the emergency brack out.
Put jack stand under the car!! I don't want to hear you got bad hurt.
Put the trans. in neutral twist the drive shaft back and forth until you find out where the slack is, it could be you pinion gear has slack in it.
Take it out of gear and grab a rear tire and turn it back and forth like a steering wheel, do booth side's till you hear or feel slack some where.
It helps to have a friend do this so you can watch the drive line its self.
Then look at your trans. mount and see if the rubber mount is gone or just wore out. then move to the yoke where the drive shaft goes to the trans.
put the car in park and see how much play you have there.

1 question douse the high pitch winding noise happen when you are siting still and not moving and make the noise when you give it gas in neutral.