Check the U bolt nuts on the rear axle for tightness, the axle can move fore & back &/or rotate with power on & off and give a 'clunk'. Did on mine after some abuse! PJB
I'd do this. Think GoMoG have a watch point article on this too.
Here's the link. scroll down to Morgan Axle U-Bolts and Saddle Plates. Talks about the "clunk" there.
