As an update. Just back from the dealers' service department. I had been booked in for car firmware update (not done), map update (not done), TomTom Live activation (now showing TomTom Traffic in lower right hand of screen) and finally to get the noise sorted as in video.
I turned up at the dealership and the noise was there as usual after a longish drive. I left the car running and went to find a mechanic quickly, but couldn't see anyone nearby. I went back to the car but the noise had gone!
I went into the service department and told the manager what I was booked in for. After waiting about 45 minutes I was told that the car was ready. I asked if the noise had been identified and repaired and he said that they took it for a drive and could not hear a problem.
I got him to get my youtube video up on his computer and he watched it. He conceded that there was a noise there but said that nothing could be done unless a mechanic could hear the noise for themselves and try to see where it was coming from. I asked if a mechanic could come for a drive with me in the hope that the noise would recur. This was agreed and after a 6 mile drive we got back and still no noise! SODS LAW!
The mechanic said that he would put it up on the ramp and see if he could see anything. He came back and said that a couple of the heat shield plates were quite close together and so he prised them apart a bit in the hope that it was the problem.... time will tell!