My 1978 wagon is making a clicking noise in the rear it sounds like it might be about to get worse and become a clacking sound. I think it might be the brake cable where it goes across the leaf spring because its just laying on the spring.

 But, after I zip tie it up out of the way if it still makes this clicking noise back there,Im going to start worrying so if anyone has had this before and has suggestions of what else to check please let me know.

 I think I read somewhere wheel bearings can make a clicking sound but I dont know if axle bearings do that too. Im going to start thinking of all the bad things it can be and worry now   Its one of those things you keep driving it but maybe shouldnt be.

This might sound dumb, but what does your differential oil look like level-wise? I don't know if clicking sounds happen there, but AWFUL sounds come from there for sure. My green '73 wagon went through two differential pans before ring gear bolts were stopped from coming out of said ring gear and being forced through the pan. Some of the bolts got mauled to death by the gears but I found out differentials don't like being out of oil. lol 

Whatever it is, I hope it's easily cured. 

 You might what to check the U-Joints.

Rear diffs growl,howl, whine, and bang but I have not heard of one clicking.I would pull the brake drums and do a brake inspection first and then work your way to the center section.I know I haven't heard every noise possable but I have heard most of them,I'm hard on diffs