Model A knocking rear end while driving

[Chrisverling]

I just was taking my 1929 Model A for a ride, when going uphill in 2nd gear I heard a strong knocking sound from the rear end. I stopped on the side of the road and the knocking stopped. Reversing into a parking lot, no knocking. I turned back downhill and the knocking started again at about 10 km/h. At home I tried to reverse a bit longer and no knocking. I have no clue what this could be.

Anyone any suggestions?

Chris