A new biker gang is roaming the streets of Richmond Hill, Queens. This crew of mostly teenagers can be seen riding along 103rd Avenue just west of the Van Wyck Expressway. The bikes roar, but the booming sound has nothing to do with engines — because there are no engines. They are ordinary bicycles, not motorcycles, although these contraptions look and sound more like rolling D.J. booths. They are outfitted with elaborate stereo systems installed by the youths.