It's not 50% unless you live in a tight-knit ricer neighborhood. It's not a trivial option to customize a car to make it louder; it takes a bit of effort.

What is true that we tend to notice annoyances more than non-annoyances, and that the car may be louder because the driver want to accelerate or velocitate more than they should, and noise is a side effect. Or the stereo is louder than it should be, not because they want you to hear it, but because they want to hear it and they don't care about you.