What causes my driveshaft to "jump" in this video?

Was just thinking about this..

If the car was on its tires, the jerking might be diferent. At present the car is supported by a jack stand infront of the spring, under the housing and one under the center of the housing.

Any of these things could change how the housing reacts.

If the car is drivable I would get a mount for your camera and take it out on the road for a short drive, watch what it does on startup and on shifts and down shifts and slowdowns.