Q: Monty, Why is it cars and trucks get tickets for modified mufflers and being loud, yet Harley-Davidson motorcycles blast out the sound without fear of Johnny Law?— Signed, a BMW motorcycle rider

OFF THE WIRE
 HEY MONTY, ARE YOU BREAKING THE LAW BY LISTENING TO THE TUNES WHILE YOU HAVE HEADPHONES  ON IN YOUR HELMET WHILE RIDING??

" but rather the sounds of classic rock as it sounds in my own helmet.
All of this in hopes that we all will enjoy the ride."

http://www.redding.com/news/2011/jun/10/harleys-roaring-pipes-test-noise-level-limits/
Q: Monty,
Why is it cars and trucks get tickets for modified mufflers and being loud, yet Harley-Davidson motorcycles blast out the sound without fear of Johnny Law?— Signed, a BMW motorcycle rider

A: With nice weather soon upon us and fuel prices as high as they are, motorcycle traffic will be at an all-time high this year, or so I'm guessing. With that comes your concern with regards to modified exhaust systems.
I wrote a column in 2009 discussing these concerns and now is a good time to reiterate what has not changed since that time.
As with most equipment violations, exhaust systems have specific limitations and requirements. I am going to lead off by saying that many people hold different opinions on how loud is too loud, but the following is what the California vehicle code basically states: "No person shall modify the exhaust system of a motor vehicle in a manner which will amplify or increase the noise emitted by the motor with a manufacturer's gross vehicle weight rating of less than 6,000 pounds, other than motorcycles, a sound level of 95 dbA (dbA is the decibel level). Motorcycles manufactured before 1970, the noise limit of 92 dbA. After 1969 and before 1973, 88 dbA. After 1972, and before 1975, 86 dbA. After 1974, and before 1986, 83 dbA. After 1985, 80 dbA."
Basically, according to the vehicle code, the newer the motorcycle, the lower the decibel level. That may not, however, always be the case. All motorcycles manufactured for sale in California meet the requirements when they arrive at dealerships. There is a section that further states that it is unlawful for any person to sell or offer for sale a new motor vehicle that does not meet these requirements.
The issue usually starts when the purchaser of the motorcycle immediately removes or modifies the factory equipment and replaces it with a system that does not comply with the lawful sound level.
There are many reasons why motorcycle owners change the exhaust system on their bikes. Performance is generally given as the reason, but the specific loud rumble of the exhaust pipe tends to have something to do with it as well. From the moment that we took a clothes pin and used it to hold on the playing card against our bicycles spokes, we wanted that noise. Regardless of the reason the exhaust system was modified, if the decibel level is above the lawful limit, quite simply, it is unlawful.
So what is a decibel? Basically it's a unit of measurement for expressing how loud something is.
Zero is silence, 130 is reported to be at the average pain level. Several years ago, I was a CHP training officer and as part of our prescribed annual vehicle code training, I procured a decibel reading device and trained officers in how loud is too loud.
There is no way that I can explain in the written word how loud, for example 90 decibels is, other that I am able to, as are most people, to know when a exhaust system has been modified to increase its decibel level. With all that being said, I have several friends who ride Harleys and the majority are all too loud and I voice my concern that they are subject to a citation.
So now comes the question, when does someone get a ticket for their vehicle being too loud? As with most vehicle code violations, the officer uses his or her discretion. I can only speak for myself when it came to the issuance of a citation. While on patrol, if I heard a vehicle in my vicinity before I saw it and or the sound caused vibration in my vehicle, I made an enforcement stop.
If I stopped a vehicle for an unrelated violation and it happens that the vehicle had too loud of an exhaust system, I would have issued a citation allowing the driver to correct the violation.
Being a fellow BMW rider, I too am aware of the excessive exhaust noise that Harleys are known for and realistically, things are not going to change until enforcement in this area does.
That being said, I will continue to ride the roadways with these soon to be hard-of-hearing friends, always riding up front as to not endure the constant roar of their bikes, but rather the sounds of classic rock as it sounds in my own helmet.
All of this in hopes that we all will enjoy the ride.