Why the sounds they heard from the car kept on reducing ?

There could be several reasons why the sounds from the car kept on reducing. Some possible explanations include:

1. The car's engine may be experiencing mechanical issues or malfunctions, causing it to lose power and produce less noise.
2. The car may be running out of fuel, leading to a decrease in engine performance and sound.
3. The driver may be slowing down or coming to a stop, resulting in a reduction in engine noise.
4. The car's exhaust system may be damaged or clogged, affecting the sound output.
5. The car may be experiencing electrical problems that are affecting the sound system or engine performance.

The text does not mention anything about sounds from a car, so I cannot answer this question from the provided context.