I'd been trying to find the location of what I thought was a dead stick rubbing somewhere underneath.

Noticeable accelerating and or turning left.

No sign of a stick but a second inspection revealed the NS rear of the underbody, centre section, heat shield had cut the black paint off the prop shaft .....phew, easily fixed......nice soft pliable aluminium.

The ? is, why did it take 18K to start doing it as the vehicle hasn't so much as run into a significant pothole or anything else for that matter.

All it needs now is a lick of paint to stop any corrosion occurring.

FWIW.

Probably a bit of road debris that got thrown up and bent the heat shield I imagine.

Just that it didn't appear bent just way out in alignment .