The A330 "hums/buzzes" if you get her much above Mach .83
So somewhere around the airframe the airflow is going sonic,but buffet due to airflow separation will occur at higher speed.
As we know some older jet aircraft suffered from jet upsets whilst knowledge of high altitude flight was being gained. So yes aircraft can high speed stall at high altitude & speed. Don't they teach that now in the ATPL?