Was there ever a supersonic flight in a non-pressurized plane, and what is/would it be like for the pilot?
When you're in the cockpit, the sound you are hearing is vibrations of the skin and canopy/windows induced by the outside flow, transmitted through the air within the cabin to your ears.  A very loud hiss/roar (even in a normal jet, if you speed up to near Vmo, say .85 M, the noise level in the flight deck gets unpleasantly loud.  Go faster, and it's the same hiss/roar but the more energy being imparted means the sound level transmitted to your ears goes up).
When Chuck Yeager was going supersonic in the X-1, he could only tell he was supersonic was by the Mach Meter, not by the noise level.
If the cockpit was unpressurized, this doesn't really change because it's still just noise transmitted from vibrations of the skins/windows transmitted through air that is stationary relative to objects it's in contact with, so you're still just hearing a hiss/roar of the outer airstream passing by, supersonic flow or not. Just way louder, I'm sure, because of less sealing and insulation.
Any other sounds originating outside you would also hear to the extent that the sound waves from that sound impacted that skin and caused a change in the sound character being transmitted through the stationary air in the cockpit.  If the wave was intense enough, you should hear a thump sound of some sort, whatever was the result the pressure wave of the sound origin changing the transmitted energy passing through the still air in the cockpit at the instant it reaches the fuselage.
The key part is that the air within the cockpit is not moving with any speed, so it will transmit any vibration from the skins, windows, engines, pumps, etc to your ears whether you are supersonic or not.