Help ID'ing a Clicking noise?

When I had an 8 1/4 in my car I started to notice the same sound, but only when driving beside a cement barrier that reflected the sound, it was coming from the back of the car. When I upgraded to the 8 3/4 I opened up the 8 1/4 and found that a few of the through bolts that hold the sure grip unit together had broken and the bolts had slid out and were contacting the bearing caps in the differential. Other than the noise everything else seemed normal with it.

As has also been said the problem could be related to a front or back brake assembly (I have also seen broken drum brake adjuster cables making a clicking sound), trim rings, hubcaps, wheel nuts etc. Have a good look at everything.