Rattle in rear end.

I have a rattle in the rear of my 2007 Lucerne, I have made everything secure in the trunk including the spare tire and jack, I believe that it is the rear brake calipers rattling, for when I step on the brake the rattle stops, I only hear this on some payment joints, it is not noticeable on all roads.

Check the trunk spring mechanism. It's two rods that provide the needed tension to open the trunk. Mine was making the rattling sound and I had to stuff a rag between the two bars. It is a ridiculous design in my opinion. The two bars clang together from road vibrations. I think that there was a plastic tie that was supposed to keep the rods together, but did not accomplish this.

I have a rattle in the rear of my 2007 Lucerne, I have made everything secure in the trunk including the spare tire and jack, I believe that it is the rear brake calipers rattling, for when I step on the brake the rattle stops, I only hear this on some payment joints, it is not noticeable on all roads.
inspect the rear brakes. if all is secure apply some disc brake quiet to the back of the rear pad shims.

The rear end rattle in mine turned out to be the torsion bars for the trunk as mentioned above. I slit a piece of rubber hose lengthwise, making sure it's inner diameter was about the same as the outer diameter of the torsion bar. After slipping the rubber hose over each bar where they make contact towards the center of the trunk, I zip tied them in place and the rattle / clanking noise disappeared. You may want to give that a shot because it is a really easy fix. LeSabre / Park Avenue used the same basic design for the trunk torsion bars, something is slightly different on this one and they make noise for some reason.