Variations in how your system sounds?


Apologies if this has been covered elsewhere.
My system sounds consistently good to my ears for the majority of listening sessions but every now and again (say 1 in 20) it sounds slightly 'off' -- not its usual self. It is a very small difference but i do hear it. I would describe it as a slight lack of focus and dynamics. This has happened through many changes of all components.
Is it my mood, or hearing variation? Do i need to filter my power? Do you have similar experiences?
mike60
I recently bought a Hi-Fi Choice magazine with a free System Set-Up disc. It's pretty entertaining, especially the soundstage tests...and it has a burn-in track with demagnetisation which I DO NOT understand...how can playing a digital track on a system demagnetize it? This will be added to the 12,416 things I don't understand, unless somebody can explain it to me.
10-13-11: Bdgregory
... Also, have you ever noticed how if you leave on vacation for a while, how sweet your system sounds on return?
This one I can certainly relate to and seem to experience every vacation. Good to know I'm not alone...
I have wondered if the eardrums can be affected by the hot water of a recent shower. Can components of the ear soften or change characteristic and take time to recover to optimum? It would seem possible, if humidity has a proven effect. Thanks for the interesting feedback so far.