Rear wheel noise during shifting

[jbpate@attglobal.net]

I have a slight "pop" that seem to be coming from the right rear during 
gear changes as force is applied to the wheels during shifting. It seems 
like there is some play in the rear axle to differential but only on the 
right side. Could this be coming from something other than the 
axle/differential?  I have original splines (good shape) and new 72 
spoke Dayton chrome wires.  The car is a 1967 BJ8 with about 78k miles. 
 Barry Pate Chapel