Had a similar issue. You may have forgotten to install one of the retainers (like #14), which will unseat the insulator (#13) and allow the strut rod to drop when lifting the car. Or the strut rod nut is real loose, but this is unlikely to unseat the spring. Only way to check is to pull strut and mount plate and see, unless you have any access hole drilled in the trunk. Or look if you have any parts like these retainers that were not installed (ref pic of anodized retainer on top of the rear shock strut).
https://www.nationalgmparts.com/auto...omponents-scat
