[Healeys] Rear Knocking noise

[PG]

Hi all,

 

I have a knock coming from my rear end that I am trying to track down.

 

It occurs only 50% of the time.  Often when jarring the car forward such as
when engaging the overdrive and sometimes when starting to take off.

 

I don't believe that it is coming from the differential but can't be
certain. When the car is on jacks and I turn the rear wheels back and forth,
I do not get a Knock.

 

The shackles are all tight.

 

Could it be the radius arm bushings??     Or the bushes on the spring
shackles?

 

Thanks

paul