Thanks guys . Wrinx/speedfreek the 156 rear seems completely different to the 155, thanks anyway
The 156 has wishbones and the trailing arm only stops forward and back movement, is not the main attachement point, it is not a trailing arm and torsion bar like the 155, no bearing just a hollow 1inch circumference tube with a rubber bush at each end, very different to 155
Symptoms, well no rear knocking as such a slight hollow sound from rear on some bumps.
Main thing is that if you grab the arm at the hub end, you can slide it back and forward (then it knocks as the washer each side of the bush hits the hub), along the bolt as it were, and the whole bush and bolt/washers moves in the hub with the arm (so dont think getting it out would be a problem! maybe fitting the new one though?). so if there weren't washers fixed either side of the bolt, it might push out
Almost like the bolts have not been done up properly. Its the same both sides so:
...maybe this play is normal to allow for movement up and down of the hub?
you can twist the arm as well, quite easiliy, the rubber seems very flexible.