I am a middle school music teacher and have much experience with
helping beginning violinists learn to adjust the bow angle, pressure,
and speed in such a way as to prevent screeching.  I am hoping that
the similarity will solve the problem with the A-string on your
instrument.

The bow speed needs to be faster when the bow pressure is heavy.
The angle of the bow can be tilted so that less bow hair contacts
the string.  My suggestion, although I don't know technically how to
achieve it on your instrument, is to lighten the bow pressure, speed up
the bow wheel, and/or reduce the amount of bow surface area contacting
the string.

My second hypothesis is that there is a crack in the body of the
violin -- at the end peg by where the chin rest would be, the bridge,
or the sound post.  One of these things might resonate in sympathetic
vibration with the frequency of A440.  If intentionally tuning the
A-string to a lower note solves the problem, this may be the issue.

If all else fails, I would recommend removing the violin from the
Violano and using a regular bow on the string.  If there is room,
perhaps using a regular bow with the violin in situ would shed light
on the issue.

Bev Ingram - Richard Ingram's wife (MMD subscriber)