mc chris is saying it's OK for girls to sleep with him because he's clean. He's had an STD test and even (an exaggeration) an emissions test - which is actually to measure pollutants coming from a vehicle engine.
when you add an amplifier and subwoofer speakers to a car stereo system the loud bass often rattles the rear license plate, which is held on with two screws. if your sound system was really expensive and loud, you could possibly rattle the car this much.
he has hollow-point bullets (they flatten on impact and are more likely to kill someone than normal bullets) and he is ready to shoot them at people who snitch (tell the police that he's dealing drugs or has been involved in other crimes).