I have asked this before under a subject of signs of early Aisin transmission troubles, but I am going to ask again after refining my own diagnosis and after some improvement following a visit to Detroit Tuned. They did a complete transmission drain and flush, but strange sounds below my feet continue to concern me.

Here's the Mystery:

a) Upon engaging reverse gear I get a muted discreet 'scrunching' sound like a stick on a slow turning fan.

b) when i let up on the gas peddle to decelerate, the car is a bit jerky with accompanying muted rattles

c) I hear those same rattles on any rough pavement or vibration source.

d) A respected mechanic at Tuffy Mufflers who had installed new ball joints a few months ago thought it might be my 'steering rack' and he was able to (sort of) mimic the sound by shaking my (also new) tie rods.
MINI of G. Rapids told him that the steering rack was not a replaceable part and was not a likely culprit.

My MINI has almost all new front end components, so the tranny is still a prime suspect except that I get no codes for it and I get the sound on road bumps as well as when the car rocks a bit with the throttle ebb and flow.

I only hear it at low speeds when things are quiet. It's not a clank as when the struts gave out, nor a rattle as when the ball joints went out.
Its a bit of crunch with a tad of shaking marbles in a muffled jar...

I'd like to fix whatever it is before I find out all at once what the H*** it was :-(

Any theories appreciated. I'm many hours from any MINI mechanics but will likely go back to Detroit Tuned (4.5 hours) later if I need an actual knowledgeable ear to take a second listen.
Mini has 98,000 and 9 years on her.