Quiet Earth,
When I made AC measurements at my house, the times where the system did not sound good correlated with the times of high distortion measurements. Usually at night the distortion levels were low (~2%THD). Also no mechanical hum/buzz from the toroidal power transformers at the low distortion times. I did not see the opposite situation when I did the measurements.
After the power company cleaned the contacts in my power meter, the noise problem stopped. I had my electrician also come in and make sure all the contacts in the breaker panel were all in good shape as part of the inspection process when this was happening.
One thing that has been discussed over time is using single phase power (220VAC/60Hz balanced) available in the US to drive systems. That is probably an interesting Lab discussion.