I noticed in the video that the shrill noise only appears on the back stroke, now is that true or was the sound out of synch on my computer? Either way is the shrill sound on yours on the back stroke as well and could that be because you are removing some of the pressure from the edge, so with the spine only on the stone and the edge just a hair width away it is allowing it to vibrate against the surface of the stone. This is just a theory and is not from any form of experience. This could cause microchipping.
I commend you for working through this on your own, but do not be embarrassed to accept help from these gentleman.

-G