I have noticed this also. My opinion is that the overall grounding configuration has been altered and does not return to its previous state until all components are turned off and then back on again. Try cycling everthing off and then back on and see if the difference persists.
Why does my system sound better??
I unplugged my stereo to change back to my old speakers. Old speakers sounded better than I remembered. I unplugged stereo again and put back original pair and they sounded better than I remembered. This is not a scientific. My question is by turning off ones stereo system do you degauss the power cables in some way. I have a PS 1000 power plant but it does not have the degauss software. I do leave my stereo on all the time. Mike