We shall see.
I think the super fast diodes and the ground loop breaker have helped remove the background noise.
When I rehoused the BB3, I added a common mode filter. The only part I did not touch was the earth.
I think (well, hope) that this has now sorted it. Noise removal in a phono stage can only lead to a better quality of sound.

If I am feeling brave, I will have to fit my XX2, but as I will have about 15 kids in the house in a few weeks time, that may not be the best idea.
I will pop an SLA stylus on the AT20 instead of the current SS to minimise the risk.