I can'r think of any mostly legal device. You would need to commit a more serious crime if you don't wish to call the police yourself. Most of the time, where you hear cRAP, you'll find crack or other illegal drugs. Even if the cops know about the noise, they usually drag their heels putting an end to it. They hope to catch the dealers, users are a waste of their precious time anymore. Only way to get some police action is a flood of calls by you and the neighbors. The police have more important things to do at the doughnut shop...
Yeah, I know you are pissed and frustrated, this topic comes up frequently, and is international. There really is no magic device you could build or use safely, to target a single stereo.
Study up on your local noise ordinance, try to gather evidence of drugs or other illegal activities. You have to use the law, or the law will come and get you. Use to be you could make your opinion known with a baseball bat, now you'd go to jail and get sued...