Have you put the shock in the hub seated correctly, could be a faulty damper, drop link tight, ball joint seated correctly, top mount fastened tightly to the damper, lock nut tight, both front coil overs adjusted to the same height, hub nut tight, lower arm bushes. It could be that now its lowered and the lower arm is sat at a more horizontal angle the rear bush could be coming out and it's getting worse as the bush is coming out?