Why does my car make a hissing sound when I go over speed bumps?

If its a quick sound that follows the deflection of the tire over the speed bump, no, you shouldn't be concerned. It is a normal sound for struts to make - its a combination of the mechanical bits moving, and the sound of the fluid going through the valving of the strut, dampening the 'hit'.

You're boyfriends a smart guy.

You know I have the same thing that, when I drive really fast over pot holes and speed bumps that the car whats to make funny noisess . I found out that the faster I drive over these things the quiter my car got ,But most of the time the tires were not proprly inflated or balaced and the susspition need work . But what I did was I took it out to a big filled and tested it and let some one drive it around so I could lision to what make funny noisess ?

yeah if you go over a bump fast and you hear a quick hiss its your shocks depressing compressed air to absorb the shock