Go back and measure your stock control arms (eyelet to eyelet) for the baseline adjustment. Are the upper or lower rear control arms adjustable or both? Upper requires much less adjustment to get the pinion to move compared to lower since lower have more impact on axle position (thrust angle) and the uppers have more impact on rotation of the axle. That makes comparing with others adjustments more challenging. The objective is to point the pinion up about 1 to no more than 3 degrees combined difference between the TC flange and the Pinion flange. So if TC is 89.5' degrees UP then your pinion should be 90.5' degrees UP (1 degree).
You can rule out pinion adjustment out as the cause of rotating spring perch angle: adjusting the pinion angle and that action relating to the position of the spring perch, the axle rotation would have to have been pretty substantial to visually notice a difference in position at the spring perch. Under normal pinion adjustment conditions we're talking a couple of degrees of movement, almost imperceptible to the eye. Anything greater would have created some pretty noticeable driveline vibrations.
Is your spring loose in the perch as it sits there? The axle had to droop so far downward for the spring to get loose, I don't see how under normal driving conditions the spring could be moving to the point of making noise unless a perch is broken, the spring isnt correctly seated, or its broken. Have you put a go-pro under there to capture the noise under motion? Are the shocks secure? The upper shock bushing should be bulging outward and rounded at the edges sandwiched between the two washers. Are the control arms torqued correctly and lubed?
