Well - my CV joint problem is solved - it was a front wheel bearing.  When
the noise first manifested itself I jacked up the front end and spun the
wheels and heard nothing.  After greasing the CV joints and spinning the
rear wheels and hearing nothing, I backed off the front disc pads,
connected a wheelbarrow wheel to an electric motor and used that to drive
each front wheel in turn.  Sure enough, the left front wheel emitted a
noise at speed.  On taking it off (next to socket head bolts, the mounting
method for the calipers has to be the dumbest piece of engineering on the
vehicle) I found some rollers on each of the bearings were  rough, enough
to cause the noise. $40 later, dead quiet.