I rolled the car into the garage and noticed a low clunking noise. With one wheel chocked and spinning the other it seems a clunk twice per revolution of the propshaft. U/J on the propshaft seems fine and it sounds like its inside the diff. If you spin the propshaft it still happens so not just on the overrun. Its an Escort rear axle, anyone any ideas?

check your crown wheel bolts. I had them come loose on my RS, they catch on the diff housing