In suburban London and the surrounding countryside, so much of the noise is caused by a handful of motorbikes that have been made deliberately, I think usually illegally, noisy. Stopping noisy vehicles would improve millions of people's lives and moderately upset a few thousand bikers. I have no idea why it isn't a more popular cause. One person doing laps of a built up area in their modified car is likely waking up…
Many "grown-up" countries do care about this. This problem is non-existant in Austria, or Germany for the most part. Roadside police checks consist of decibel metering, which they are trained to use. They will impound the vehicle on the spot if its over the legal limit. Even race tracks have strict sound limits, the scrutineering process has a sound measurement part.
This is highly dependent on where in Germany you are talking about. In some parts the police don't care at all.