Motorcycles are allowed to split lanes under certain conditions, one of which is that it must be safe to do so.
If there isn't room to split lanes, it obviously isn't safe to do so.
"Lane splitting by motorcycles is permissible under California law but must done in a safe and prudent manner. The motorcycle should be traveling no more than 10 mph faster than surrounding traffic (without exceeding the speed limit) and not come close enough to that traffic to cause a collision."
Noise Restrictions
23130. (a) No person shall operate a motor vehicle under any condition of grade, load, acceleration, or deceleration in such a manner as to exceed the following noise limit for the category of motor vehicle within the speed limits specified in this section:
(2) Any motorcycle other than a motor-driven cycle at a speed limit of 45 or less..... 82 dbA. Any motorcycle other than a motor-driven cycle at a speed limit of 45 or more..... 86 dbA.
(b) The noise limits established by this section shall be based on a distance of 50 feet from the center of the lane of travel within the speed limit specified in this section. The Department of the California Highway Patrol may provide for measuring at distances other than 50 feet from the center of the lane of travel. In such a case, the measurement shall be corrected so as to provide for measurements equivalent to the noise limit established by this section measured at 50 feet.
23130.5.
(a) The noise limits, within a speed zone of 35 miles per hour or less on level streets, or streets with a grade not exceeding plus or minus 1 percent, shall be:
(2) Any motorcycle other than a motor-driven cycle..... 77 dbA.
27150.8. The manufacturers of motorcycles and motorcycle accessories shall certify to the department that the exhaust system is in compliance with the standards and regulations adopted by the commissioner.
27200. (a) The Department of Motor Vehicles shall not register on a dealer's report of sale a new motor vehicle which produces a maximum noise exceeding the applicable noise limit at a distance of 50 feet from the centerline of travel under test procedures established by the Department of the California Highway Patrol.
27201. For the purposes of Section 27200, the noise limit of 92 dbA shall apply to any motorcycle manufactured before 1970.
27202. For the purposes of Section 27200, the following noise limits shall apply to any motorcycle, other than a motor-driven cycle, manufactured:
(1) After 1969, and before 1973..... 88 dbA
(2) After 1972, and before 1975..... 86 dbA
(3) After 1974, and before 1986..... 83 dbA
(4) After 1985..... 80 dbA