Noise doesn't change with fan speed and it's only when the fan is on.

https://photos.app.goo.gl/AmYyCkPWGUXdFWam8

 

I am going to go for a bit of leaf or debris ingested into the fan and touching the blades as they rotate.
I had been wondering about the climate control system aspirator, which is a tiny fan which draws air over a thermocouple to determine the cabin temperature, but it looks as if your car is LHD, and I think it is always located in the RHS knee area. It has a plastic cover about an inch square, and is worth checking anyway, as the thermocouple will likely be covered in dust and would benefit from a clean

 

The aspirator is on the left on LHD cars. It does get dirty and can be audible. Only used when the climate control is on. Take off lower left panel below the dash vent to clean. It has a disconnectable wire lead.

 

It was the temperature sensor fan. Tried cleaning it and put a drop of motor oil on it but it's the same noise.