carrier. The rear suspension is also mounted to the subframe. The subframe is attached to the body at several points that are rubber. That whole assemble can do a little dancing, especially as the rubber mounts wear and weaken with age. The whole assembly connects to the motor/trans cluster via the two piece drive shaft. Movement on the subframe cannot be transferred to the engine/trans because the spline shafts slip in the longitudinal direction.
So my guess is that shift column movement during on/off throttle, is likely a result of softening of the 3 motor/trans attachment rubber mounting points.