2 updates from me:
Response from Van Nicholas : With the handlebars we supply an adhesive sandpaper which is meant to be applied under the shifters. The handlebars are 22.8mm thick instead of the standard 23.8mm handlebars and this sandpaper is meant to fill that space. If you have applied mounting paste to the handlebar, tightened it to 10nm and mounted the shifters correctly and the noise remains, I recommend you to take your bike to a VanNicholas dealer or another bike specialist.
I will put the Van Nicholas bar bar on and try with the mounting paste. This see as the easiest, best and cheapest option - after all I have all the bits (although I need to work out what mounting paste is - anyone?)
From Gilles - 128mm of drop sounds like it should fit… but despite the more important drop, I know it can be difficult to fit the shifter on some bars. I know Nitto randonneur, Rene Herse Maes work. Ritchey bars with "classic bend" seem to work too. I’ve also tried a Deda Speciale we have here and I managed to slide the shifter up to the to section.
Nitto and Rene will be my "plan B"
I bought Ritchey Comp Curve Road 31.8 Handlebar - 2020 - BB Black. This looks like it has a "classic bend"..... The shifter does not fit around the bend

