Lately I had a number of interesting observations. When your bike is properly maintained, it creates a specific sound pattern when you ride it. Most of the time you can hear your tires rolling off the tarmac (depending on the tire profile, a different type of sound) and you can also hear the chain going through your derailers [sic!]. In my case I can also hear my spokes in the wind because they are flat and cut the air. That’s usually all you should be hearing and for the most part it stays the same. Often, you can’t even hear the chain, just when you pass a wall or cars then the sound reflects back to you.
now due to this unchanging nature, your brain starts to get that pattern and you are able to figure out irregularities.
One of the irregularities for me was that the chain seemed to change the sound pattern. It was still constant, but it had a different pitch. This is interesting, because it means that it probably affects the whole chain. What might be the cause of it? Applying Occam’s Razor you come to the conclusion that the simplest possibility might be the chain needed lubrication. So I put on some oil and lo and behold, the sound pattern returned to the well known “correct” humming.
A different example of this was when my bike started to make an irregular rasping noises. Like thread against metal. The sound seemed to come from the back, further back than the rear dereiler. The prime candidate was the wheel, which extends a good deal behind the dereiler. The only thread I could think ok was the threading on the valve. So after screwing on a counter nut on the valve (which I did not de before since it was not a problem), the noise went away.
So you see, listening to your bike is a great method of debugging.