Quality of Power

[yanc]

Apologies if this has been asked for below ....

At times I think I have a most excellent, articulate, crystal clear, specious, heart warming system ...
But there are hours within the day (hard to be exact) where music sounds flat, and unbearably warm, almost glowing unnaturally.

I can only suspect the quality of electrical current coming in varies during the day.

Is there something I can do to prevent this?

Or
Anything else I should be looking for ...

P.S. This is regardless of quality of power cables