Finally found the problem ...
my RH rear tyre has started to delaminate under the tread - it shows up as a discernable line across the tread face where the belts overlap in the carcass itself. The circumferential belts had started to separate under the carcass/tread rubber. It was this that was making the sound when driving along and had me fooled into thinking it was a mechanical (eg: bearing) noise - once per wheel rotation.
The tyres are RS3 that are coming up for 2 years old and since we heading into winter here, they have been given a bit of a warm-up as I exit my driveway each morning for the last 4 or 5 weeks - which I can do now that I have my yaw sensor power isolation switch installed - have been in the habit if lighting them up each morning as they were not worth a pinch of goats-cr4p from a grip perspective otherwise. They were still OK if I could get heat into them, but diabolical when cold.
However, seeing the line across the face of the tyre, they had to go !!
Both rears now replaced with Direzza DZ II.
Oh well .....
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