Last night, I was sitting thinking about the trip to the dealer to investigate this noise.
I suddenly - and I don't know why! - decided I thought I knew what it was, so I went straight to the garage, in a state of considerable undress (yes, I know, too much information...

) and fixed the noise in 30 seconds.
It had happened before, you see, a year ago, but my aged memory had forgotten. (Why can I always remember the word "Alzheimers" whenever I try, but I forget everything else?)

The answer, the thing that made all that noise........... One of my headbolt bridges was ever so slightly loose! Got maybe 1/8 of a turn with the Allen Wrench on both screws. Loose enough so you could just feel movement in it, tight enough so you wouldn't notice, except for the noise. As I say, it happened a year back, both bridges, seriously loose, but I'd just forgotten. Such is old age......
I did still go to the dealers though, to complain about the MAJOR cupping on both front and rear tyres!
Jim