System sounds different at different times Why?

I have a perplexing and cofusing situation. Im convinced that during the day light hours the response of my system is abnormal, subtly so or not: bass is reduced (the amp doesnt even get warm at high volumes) its not as clear or tight, imaging and separation are not up to snuff, mids sound forced and crunched but sometimes/usually in the late (after midnight) evenings everything sounds like what I expect... Im never sure exactly how much of a difference because Im not sure if its occurring or not, its sometimes very subtle. When its extreme its obvious. I cant AB day to day to much time in between listening sessions As far as ABing day to evening , I can be listening at moderate levels during the day and late into the evening thinking ok no changes This is what it is supposed to sound like anything else is me. . Change a CD or the next track will play and suddenly wow that sounds completely different. Low end blossoms separation and staging are superb. Even my GF heres the difference. No rhyme or reason appears to be completely random and arbitrary. The only constant is that it just never sounds right during daylight hours. Usually
Worse, I have no point of reference.
heres what I got what troubleshooting Ive done. CAL transport, Monarchy DAC, Bryston amp B&W 802 Matrix 3 bi wired (which are for sale by the way) and a jitter box.I have switched from unbalanced to balanced sends, coax, optical balanced digital sends,cleaned connects, flipped flopped substituted yelled at cables used a tone generator to listen to tones and sweeps (useless by ear just as useless with crappy mic on pc) Looks like 1k sounds like 1k so...Tried a couple of Hail Marys. No definitive results.

Besides ambient temp Im now thinking its a power delivery issue. Hundred year old apartment with grandfathered ac. I get 120 at the outlet wired correctly but i have about 23 v between neutral and ground No voltage drop when stereo is on but when turn on a motor on same circuit (say a fan) drops about 3 volts Ok That was a lot of typing Any ideas? thanks
mc