OK took the rear wheel off for a proper inspection. Now I'm steaming mad.
9 repeat 9 loose spokes that move freely and rattle - one is so bad it has come detached from nipple in the hub and is missing the nipple. Mileage 4007, last service 2 weeks ago at 3700 in dealership. I'd love them to explain how 9 spokes suddenly workled themselves so loose in 300 miles - when checking them is a service item afaik.
I don't bump kerbs, don't go off-road and don't ride it particularly hard either - ( I have other toys for that
Rest assured the bike (nor I for that matter) will be going back there.
Lesson learned - don't buy bikes with spokes, and if you do check them before every ride.
This 'one will be traded in next July - maybe something different this time.