AC squealing (and a lot of other noises that are somehow synchronous to the grid frequency) would be a slightly off G outside of North America (slightly to high

AC squealing (and a lot of other noises that are somehow synchronous to the grid frequency) would be a slightly off G outside of North America (slightly to high, G is ~49 Hz and the grid frequency almost everywhere is 50 Hz), no need for perfect pitch to guess that. In North America (60 Hz grid frequency), I'm not quite sure whether one would recognise it as a A# (58.3 Hz) or a B (61.8 Hz).