It would appear that weather plays a large role, with wet conditions and low pressure systems being quite bad for the sound, the electrical grid most likely being affected. It would also appear early mornings and nighttime are better times for critical listening. It's difficult to prove other than by tracking sun spot activity over at the National Weather Service site, but sun spot activity might influence the sound, I wouldn't be surprised. Not to mention the myriad things we change in the system without paying much attention. What ever happened to keeping a log of changes we make, even seemingly innocuous changes, like arrangements of cabling, absolute level for the turntable or CD transport, etc.?
