System sounds better at night?


I have noticed that my system sounds MUCH better at night, after about 10pm than at any other time of day. It is clearer, more open and transparent, with a blacker background. Another audiophile told me that this is not real, it's just that there is less noise in the household at night. I disagree in that what I hear (or don't hear) is not simply due to less ambient noise but rather cleaner sound. Will power line conditioners simulate these effects during the day? Has anyone else noticed this and what is the most effective way to get better sound during the daytime? Serious responses only, please.
jc4659
It could also be the giant EMI emitter is on the other side of the world  ;) 
No solar flare or sunspot activity at night, much reduced seismic vibration due to automobiles, buses, subways, less cell phone activity.
Interesting to see my OP from 2001 and I still feel the same way about day vs nighttime listening.  While I have not found a line conditioner I like, judicious placement of an isolation transformer has helped.
@celander  Did you purchase in US and if so from whom?  I'm guessing this is $$$.