Sounds like out & out BS to me...How about all those friggin' Harley Hogs that are WAY beyond any sound level meter?
Sounds like the cops in your area have nothing better to do.
I have my exhaust on my '70 Z/28 dump out behind the rear axle and I ain't changing a thing.
My '69 Z/28 has cutouts with side pipes so when I go through our local tile-lined tunnel,I usually enter in 2nd. gear around 5500rpm and then accelerate from there to about 7-grand...the look on those drivers around me...?
PRICELESS