When the volume of the sound is low, Adam walks home from school. When the volume of the sound is high, he gets a ride. Why?
The sound is a body of water.
When the tide is low, he can walk.
When the tide is high, he goes via boat.
Other reason can be: Adam is blind When volume of sound is low, he can navigate by hearing, and he walks When volume of sound is high, it becomes too difficult to understand what's around by hearing, so he takes a ride.
As you state in the question:
When the volume of the sound is low, Adam walks home from school.
Adam's parents drive him on their way to and from work during [noisy] rush-hour traffic (every morning and possibly some evenings). When Adam finishes school before the evening rush hour while his parents are still working, he walks home.