This would be from your axle bearings. You will notice the clicking as you brake and at slow speeds if you leave you'r window down and drive beside something that reflects the sound back at you. The axle bearing have no inner race and the rollers of the bearing ride directly on the axles themselfs. My frined had the same problem and we replaced both rear beaings and seals and the noise went away. Although I recently had the same problem and decided since I had the axles out I would upgrade to Moser engineering axles and Moser bearings, my clicking has been reduced but not completly gone. I blieve the clicking is from the axles falling between each roller in the bearing as there is some clearance between the axles and the rollers in the bearing. You will need a slide hammer rear axle bearing puller if you decide to change them.