Rick Holtsclaw is doing and continues to do great work on this.
Nationwide there is little success so far. As a former motorcycle dealer I am 100% against this narcissistic attention getter.
We (in the Bay area) may be better positioned to address the issue, San Francisco sees itself as a social and legislative pioneer. Often things start on the West Coast and spread throughout the world. Smoking bans in bars and restaurants for one. At the time the success of that initiative seemed impossible.
A major point, the exhaust noise magnifier is close to the ground level. Closer to the ears of children.
The noise is far over the level that will damage their hearing for life. If we are concerned that rock music will damage adolescent ears then this noise is many times louder, involuntary, and down at their level. If you worked in a factory this noise level would violate OSHA. Infants are exposed to it all the time.
Another complicating point, (Rick may back me up on this). Many cops are sympathetic to the noise, even supporting it. Worse, my estimate is the average police motorcycle in San Francisco has illegal sound from its muffler. Keep in mind (as a former dealer) this an act of commission not omission. A mechanic had to alter the police bike intentionally to make that sound. The bikes don't come that way. So step one is to get police compliance. Any way right on let'S do something.