Well little things can be hard to find.
I have been chasing an annoying, worrying rattle/vibration,
when in reverse.
Sounded expensively like the auto needed work
With a bit of help from normal hearing people at our club meeting,
we found it was most likely engine mount related.
Found it today,
It was the nut that holds the CAT to its bracket, had come loose.
So it was related to engine movement.
Will probly get new engine mounts anyway,
cos the engine was moving a bit much.