w123 banging from the rear

[sceh]

I know this subject has been raised before but I can't find an answer that fits.
I have a 1981 240td with SLS. 80k miles from new.
I have tested the SLS and changed the spheres - works perfectly. Changed the anti-roll bar mounts and connecting rods. Changed the front suspension mounts of the subframe. The CV joints look perfect and have no leaks and no movement. The exhaust has all the stops and when under the car it can be shaken hard and does not touch the bodywork anywhere.
The subframe rear joints look perfect and have no movement with a big crowbar.
The tank is not loose and there is nothing in the boot.
The bangs occur at very low speeds with the slightest bump and don't really get noticeably worse at higher speeds. The sound is hollow and random.
What on earth can this be?
I have not changed the differential mount. The sounds seems to be centralised and not to one side - which might indicate a shocker.

Any ideas welcome!

 

[Stratman]

.. Wrong thread

 

[sceh]

Good condition and well mounted with no movement causing it to hit the body. Rubber bumpers all in place

 

[sceh]

No, it could be a tank baffle. Does anyone have a diagram of how these a mounted? Would it still rattle if the tank was full (or empty)?

 

[a111r]

Perhaps someone's put one of those 'Broquet fuel catalysts' in the tank or some other cranky nonsense?

 

[sceh]

no - I have been the only owner