That rumble rolling up valley roads on warm summer evenings is sweet music to some -- and a buzz-kill for others. It's the roar of motorcycles, revving at stoplights and thundering up and down the street, bouncing shock waves off buildings like the soundtrack of a 1960s biker movie.
For some motorcyclists, the noise is as much a part of the riding experience as fresh air. Harley-Davidson even sought to patent the "potato-potato" sound of its engines a decade ago.
Some riders pump up the volume even more by removing stock catalytic converters and adding aftermarket pipes in search of better performance -- and an ear-splitting roar that can infuriate patio diners or sidewalk latté drinkers.
Some bikers revel in the sound, and others justify it by saying it protects them from inattentive motorists. "Loud pipes save lives" is their mantra.
Nonsense, says Fresno motorcycle police Sgt. Eric Eide, who rides an ultra-quiet BMW.
"Straight pipes are hugely offensive," he said. "It's a quality-of-life issue."
Noise "is one of those things that needs to be addressed."
That appears to be happening. A proposed law working its way through the California Legislature, Senate Bill 435 by State Sen. Fran Pavley, D-Agoura Hills, targets modified motorcycle exhausts that produce more air pollution.
The bill also aims at the extra noise generated by after-market motorcycle exhausts.
Spoiling power, freedom
"That's going to spoil all the fun," said Chris Prendeble, a Hayward resident shopping at Mitchell's Modesto Harley-Davidson on Carpenter Road Sunday afternoon.
"I'm planning on getting a nice big, loud (bike)," Prendeble said. "Preferably you take 'em and tilt the pipes down toward the street. That really makes 'em pop."
Altering exhaust pipes isn't just about making bikes louder, Prendeble said. It also amps up a motorcycle's power, which is important because "otherwise, Japanese bikes leave you in the dust."
Robert Walsh, a 52-year-old Modesto resident looking over a silver bike at Modesto Yamaha, said the proposed law was another case of the government trying to rein in freedom-loving bikers. Although some bikers make their rides louder purely for "narcissistic" reasons, Walsh said, it's their right to do so.
Walsh himself prefers a laid-back, moderate rumble to an all-out sonic shock and awe. He wears a helmet, but he's opposed to helmet laws, which he says are another example of lawmakers intruding on biker rights.
"The more they keep taking our freedoms away, the more rebellion there's going to be," Walsh said. "What are they going to do, run around with decibel meters? There's better things they can do with their time."
Safety and sleep
Other bikers said they understand what's fueling the proposed law. Harley rider George Hamrick of Atwater, in a black leather vest and a flame-print head scarf, said "straight pipes" sometimes wake him up at night, so the proposed law could be a good thing.
On the other hand, he changed the pipes on a Suzuki he owns because he wanted the bike to be louder. He said he did it for safety reasons so drivers can hear him coming and to improve mileage.
Some motorcyclists are trying to emulate the outlaw biker lifestyle through loud exhausts, faux Nazi helmets and skull facial masks, Eide believes.
He said officers use a vehicle code section to cite motorcyclists for excessive noise but generally go after only extreme cases.
It isn't always easy for police to make noise violations stick. Mary Lynne Vellinga, a legislative consultant in Pavley's Sacramento office, said the standards in the current law are not clear and tickets may not stand up in court.
She said her research shows that California Highway Patrol officers wrote just 14 citations in the past two years.
Pavley's office wants to strengthen the law and, after an initial setback, is still fine-tuning a bill that would do so, Vellinga said.
A portion of the bill that would require semiannual smog checks for motorcycles appears dead for now, but Vellinga said Pavley's office still intends to use SB 435 to target motorcyclists who remove catalytic converters.
'Super-vocal' told to hush
Under current law, a motorcyclist cited for removing a converter often can ride home, bolt the stock exhaust back on and have the citation cleared.
That would be much more difficult if smog checks were required, because many riders would need to have expensive engine modifications done to pass a tailpipe emissions test.
Vellinga concedes getting a law through the Legislature has been a tough slog.
"Motorcycle folks are super-vocal," she said.
But industry officials are aware a backlash is looming. Harley-Davidson President Jim McCaslin, in a message on the company's Web site, told riders to pipe down, citing a 400 percent increase in negative news stories regarding motorcycle noise in the past 10 years.
Modesto Bee staff writer Leslie Albrecht contributed to this report.