Transmission goes 'boing'

[Zeke3]

Kevin, I have a non-Ford car that had a squeak like noise that turned out to be the splined connection between the axle and a universal joint. I am thinking your noise might be the splined connector between the drive shaft and the pinion shaft at the differential. There was a picture on here not very long ago that showed excessive wear on a splined coupling. Good luck with your search.