The Bourns inductor is in place.
It is worse. Voltage is very unstable, duty cycle is ~70%. And the hiss is still there.
The weather is very hot.
I have anticipated the result : I have an bigger inductor to try, but I think the culprits are the capacitor. For some dielectrics, the temperature sensitivity is way more important than the inductor permeability one, and the piezoelectric effect could explain the hiss more effectively (and the Brouns inductor is supposed to be shielded).
I have ordered some (expensive) 10nf 1Kv C0G capacitors to try. They were not in stock, estimated shipping mid november…
The next days are suppose to be colder. Will see the result.

You could follow the results on the website : unit 5100005F