Rear end clonking 240td

[sceh]

1981 240td with 120k kms from new.
When driving slowly over bumpy and not so bumpy ground (like my driveway exit) I have a loud clonk from the rear (estate car btw). It is not a regular knocking either.
I have checked everything I can move by hand and stripped and checked the self-leveling suspension and changed the spheres. It works perfectly.
Any ideas? What should I check next?

thanks for any pointers

 

[sceh]

If I replace the front rubber bearing of the rear axles, is it a straightforward task? Anything I should be aware of?
thanks

 

[SLKNick]

Could be almost anything: Exhaust system, suspension bushes, broken spring (can be hard to spot), anti-roll bar bushes, spare wheel or jack jumping around the boot ....

 

[sceh]

For the front rubber bearings the first thing you should do is burn the Haynes manual if you have be daft enough to buy it.
The problem is that when you remove everything, the subframe moves relative to the body so when you come you re-install the bolt, it is misaligned. Getting the rubber in an out is the easy bit but the misalignment is currently defeating me on one side.
I tried wedging everything in place when I removed things but it didn't work on one side. I used wood but metal may be better with glorious hindsight!