The Home Office collects and publishes data on Fixed Penalty Notices and other outcomes for motoring offences, including wider offence category. The most recent data is available here:
Data on the number of penalties for traffic noise offences, by year since 2016, has been provided in Annex A.
However, data is not collected specifically on penalties for illegally modified exhaust systems.
Annex A (xlsx, 13.3KB)