Two days ago I did a new bios update on the notebook.
The process worked fine as usual and, again as usual, did not fix or improve the issue with the fan noise.
After 36 months with it I have to bear it for only 12 more months until the notebook is due to refresh.
A positive note about the 6430U: it does no longer trigger the security scanner in the Ben Gurion airport. Whatever the chemical that was there it is now completely evaporated.