Why do people turn the car stereo down when they are looking for house numbers?

To eliminate distractions in the environment to better focus on the task at hand.

I also do it when I get lost and am trying to find my way. I think it is just something we do so we can focus our concentration more easily.

To listen for the house to address them!?

If others are in the car, then the driver would be able to better hear those in the car with them to say something…

others can include schizophrenia

Because they realize they can’t give the music the attention it deserves right now.

The others are correct in that turning down the volume is sort of like channeling energy to the eyes from the ears. Also, I find myself turning down the stereo whenever I might be rolling down the windows (easier to see house numbers, street signs, and so on) in order not to disturb the neighborhood.