years ago, dad got a ticket in his 69 z28, for un-necessary noise. it had chambered exhaust on it. he fought it and won. he called the illinois epa and found out that the z decibels allowed was up to 85. also it had to be measured no more than 25 feet from rear of car and no more than 2 ft lt/rt of the centerline of vehicle. also no more than 30 mph speed. at that time, the only place that had a decibel meter was the shell refinery. he has all his paperwork in hand when he went to court and the judge threw it out. funny that the officer that gave him the ticket later became the chief of police and him and dad are really good friends. epa should have all the info and procedures for measuring noise.