Even when Hector Tabarez, 25, keeps the windows rolled up as he drives his 1985 chocolate brown Nissan pickup, his reputation precedes him. Anyone within a several-block radius can hear Tabarez coming, for he drives what is known as a "boom car." The auto mechanic from Gardena, Calif., spent $8,000 to install the vehicle's current stereo system, which comprises a deluxe Alpine 7902 compact-disc player, two heavy-duty Orion amplifiers and 32 speakers. His rig can deliver a bone-jarring 144 decibels of sound. "I just got carried away," he admits.
Tabarez is not booming alone. Across the U.S., thousands of young, mostly...