Side issue - The Criminal Defense (CCDB) listserve I'm on had a posting concerning a non-checkpoint 'checkpoint.' At issue was the fact that only vehicles stopped at gauntlet were motorcycles, whereby some (unnamed) agency rep would come out and examine bikes' pipes for EPA markings. Of course the issue really at the heart of the posting had more to do w/ the subsequent DUI (and the fact the rider given the DUI experience was Black) than noise, but it means that Denver and metro agencies are out for you, if you're trying to save lives (w/ loud pipes) - especially your own.
My question would be, what about those bumblebee Hondas, or other vehicles that scream, "HEY, 'MIDAS'-IZE IT!!!"