They don't, most race series now run to the same noise limits as cars on track days. Blame the government, the EU `uman rights act, and circuit owners for not fighting noise restrictions by pooling resources and having a proper court case. Most objectors to noise from race circuits are "incomers" who chose to buy properties bordering circuits at their perceived market value, then decided to object about noise levels, possibly with compensation in mind... You can't beat them (at least not until we get a dictator in here to sort the stinking mess the country is in), so if you love driving cars fast, and value your licence, it's best to keep the blood pressure low with a decent exhaust and intake system