A lifeguard claims he was fired for refusing to wear the proper uniform. Is it important?
Have a friend ride with you and see if they can narrow down what part of the car it is coming from. You can also have them stand on the curb and listen while you go back and forth over a speed bump. Once you have it narrowed down, you can start searching for loose hangers on the exhaust, or loose sheet metal on the body, or wherever else the noise is coming from.
With the lack of information in your question, I'm going to say it's the city, or the property owner. Speed bumps are great for slowing people down. They should be used more in high pedestrian traffic areas and neighborhoods.
