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
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 $$$.
A lot of RF is airborne, that why cell phones work indoors, and generated by microprocessors in electronics so power conditions isn’t going to help that. Just saying. 
Daytime enjoyment of one’s audio system is hampered by so many things. Solar radiation, demand on the power grid of local utilities, consumer products being used in home, increased airborne particulates, etc.