'Clicking' in reverse only

[thatoneguy]

I have a '70 F-100, 302/C4 that has developed a new noise. I noticed it yesterday after driving to Kirkland and back, there is a repetitious 'click' when I am stopped with the transmission in reverse. I have not been able to dig in and test it much yet, I will update this once I have been able to. I did not see if it is at speed or just when stopped, heard it after backing into the driveway and decided to let her sit there until I could diagnose.

For now, I wanted to see if anyone has encountered a similar issue and had any ideas as to the issue. Transmission is about 2 years old (I would estimate under 5k miles) and the third member is freshly re-done with a new posi. U-joints is about the only thing I can think of which would be directional, anything else I could think of (torque converter, flex plate, engine noise) would be present regardless of the gear I am in (or at least in my mind I rationalize they would be).