Up to G3 is not bad but when I play like A3 and B3 they sound shrill and horrific. Is this just me, my Yamaha YFL 381 flute or both? What do these notes sound like on pro model flutes in the hands of a beginner?

Do you mean A6 & B6.

If so fingering is different than lower octave notes.

Check:

http://www.wfg.woodwind.org/flute/fl_bas_1.html

I couldn't tell you without seeing you play or looking at your flute.

Let someone that plays very well, play the notes on your flute. Then, you'll know if it's the flute, or you'll know what to work toward.

Do you mean A6 & B6.

If so fingering is different than lower octave notes.

Yes those notes. Sorry!