I don't think what you are hearing is due to the voltage cutback. Any power supply work its salt has enough voltage regulation to maintain it's output voltage through a 6% drop in input voltage, which is all you are seeing.
IMO the more likely culprit is what is causing the power company to lower the voltage in the first place and that is the fact that everybody and his brother is running their air conditioning at full tilt. Refrigeration units are notoriously noisy and push all kinds of noise back into the power grid. I would think all the extra trash riding on your commercial power is much more likely the cause of the grain and hardness than the fact that your voltage is being lowered by what is really a rather small amount.
BTW, I just looked at my AC voltage and it is only down 1 volt, to 119, but today has not been as hot as the past few and I really should look at it during the day, when the commercial and industrial load is on the grid.