Some players produce a beautiful vibrato, played in the pressure window just above the croak and just below the clear high A.  It takes some very steady blowing and at the exact pressure to get these sounds.

Sometimes the high A is just too rough, and the crow needs to be reduced. Try sanding the very tips on a flat surface with very fine sandpaper, 320 grit or above will work. Hold the reed at an angle of around 35 degrees and wipe each side of the reed once. Re-test in the pipes and repeat if necessary, taking care not to sand through the tips.