The 'too low altitude' warnings for flaps and landing gear,  need looking at.  They are activated even on takeoff, and thus become a nuisance and distraction.   Can  they be turned off ?

Yes. Look at the buttons just above the Baro knob.

Right !!!     Thanks

I've also noticed an extremely annoying horn if you're below 2500AGL and below 50% RPM without wheels down. Haven't found a way to disable it other than increasing RPM, so if someone has an idea on that, I'd appreciate it.

There appears to be no gear silence from what I can see on the internet pictures of the cockpit (in the real one I believe it's on the left side of the left power lever).

 

Maybe try going to the root Sound folder and renaming the file?

 

For instance with their SR22 which I have the main sound folder is here:

 

B:\Prepar3D v3\Sound\Carenado\CarSoundSR22T

 

I'd guess the B350 folder is in that same area.

I asked my friend and he said it is present in their model... it is where the real world one is (which would be tricky to get to without track ir or change of viewpoint)