Well some more revelation today:
1. appears to only happen over 50kph
2. nearly always happen during gradual acceleration between 70-80kph
3. happens intermittently above 80kph even at constant throttle
4. never happens when coasting
Had the car up on a lift and can replicate the same sound by accelerating in any gear (easiest to hear in 4 or 5) to about 80kph then SIMULTANEOUSLY tapping the brakes.
The sound is isolated to the LEFT (driver) rear. The axle shaft on that side is looser and has a lot more lateral play than the right. Upon the "move", it appears the shaft moves outwards (as it should) and the sound occurs ALONG with a very small drop is speed/rev. This may be due to the inherent friction slowing that drive wheel down (?)
A rebuild of the axle and replacement hubs are on the list.
Having said that, would this cause added brake dust on the RIGHT front? That is, the complete opposite end of the car? Could it interpret that speed difference there and actuate the opposite front brake? There is definitely increased brake dust on that side which may or may not be a symptom.
Having a data logger and watching the wheel speed through Autologic (cannot monitor ABS when driving), there doesn't appear to be any change in speed per wheel. Not noticeable at the resolution and sample rate it's running any way.