Hey, this is to the ones around here who sleep sometimes. When some noise is on and you are about doze away without turning it off, does it get strangely...louder to you? I remember I fell asleep while the Empire Strikes Back was playing and a TIE fighter just got BLARING loud for no reason. No volume difference for the rest of the movie, just when I began to slip into dreamland with a pink puff ball and a fat penguin king.
I know that the human ear picks up frequencies on some kind of a curve. So it's easier for us to hear some tones than others. Which means that some sounds seem 'louder' at the same volume as others. Perhaps that's it?