I once measured the silence in my listening room atop that mountain and found it to be (from my best recollection) about 23dBa. At this level, if you are still enough, you can put your arm up to your ear and hear the blood pulsing through your veins. If you breathe normally, you can hear the air move in and out of your nose. Then the refrigerator upstairs would turn on or the hot water pump for the baseboard heating would turn on and drown out this amazing silence. As the saying goes "It's always something" and I got used to turning off the heat when I wanted to seriously listen for a long period of time.
Now I live in a small, rural community in the middle of a golf course, and although pretty quiet, still nothing like it was atop that mountain. The challenge one has to hear silence is that the more quiet the background gets, the more annoying everyday conveniences appear.
When I first moved to the mountain, I turned on the stereo I was completely happy with while living down in Denver. But after a few days of unpacking and arranging the system, I noticed the hum coming from the speakers. It was always there, but the background noises of the suburbs drowned out this low-level hum. Now truthfully, it wasn't much, but just as it is with an annoying light, once you notice it, you become obsessed to eliminate it.
The hum was coming from my old McIntosh 2100 power amp as identified by disconnecting the interconnect cables between the preamp and the power amp. This was one of the first solid-state amplifiers McIntosh designed during the transition from tubes so many of the practices used in tube design were employed in this SS model. I had had this amplifier since college so it was now six years old but otherwise functioning flawlessly. So I went to work to find out what was going on.
To make a long story short, it turned out to be internal ground loops built into the design. Changing the grounding everywhere to a true single-point ground configuration made the noise level essentially disappear (started with a S/N ration of about -86dB and ended at about -105dB). What I noticed when I turned it back on and plugged it back in was that yes, the hum disappeared as expected, but something else came alive. I heard details I never knew were there and the only thing I did was eliminate the ground loops in the amplifier.
Years passed and each piece of equipment in my system succumbed to the soldering iron and wire cutters. Each time, this same improvement was observed with no other changes to the system. Taking this a few steps further, I investigated the house wiring, line conditioner wiring, chassis leakage, interconnect cable grounding, and speaker wires for similar effects and each time I eliminated ground loops the results were exactly the same.
What started out to be eliminating an annoyance turned into an investigation in removing effects built-into the system. Some of these can be easily eliminated (house wiring, chassis leakage specifically) but the others require a lot more work and an understanding of circuit designs.