I worked at a plant that used 20 megawatts power. We would use a transformer and run 480V through the plant. We would see spikes of 600V. So yes, our grid is not a smooth thing. Air conditioners are notorious for ground faults. Dirt in circuits causes "tracking". You have to have an ultrasonic listening device to hear it. Variable frequency drives put out very dirty power. So if one plant does this, think about the community as a whole.. I would go with the difference in the grid as to why your system sounds better. Surprised someone hasnt come up with a cleaning and regulating device, or I just don't know about it.
DISCUSSION: "It only comes out at night". Does anyone else have this experience!?
In my listening experience, whatever system you have, whatever components, whatever the material, medium, one thing always seems to remain constant. It ALWAYS sounds better in the deep and still of the night!!!
Is it because night time is generally quieter? Is it because the world of electronics is then shielded from the SUN? Is it because there is less demand on the electrical service?
Whatever it is, there is one thing I know for sure, music sounds better late into the night!