I've just DIY some springs onto the car and everytime I go over a hump, a knocking sound comes out from behind the rear seats. I tried to replicate the sound by bouncing the car up and down and left and right but I couldn't get the sound out, only happens when the car goes over a hump or raised part of a road.

I've doubled and tripled checked all the bolts and they are tight, the springs are sitting nicely. Only thing I need to mention is I had to remove one of the rear linkages to remove the whole spring/shock assembly but that's about it.

Any ideas what that could be?

THANKS!!!