Why is my Saab 900 squeaking?

Could be something in need of lubrication, when's the last time you had it serviced? There's lots of parts that just need to be kept greased or they'll start squeaking. As the car hits bumps, all kinds of parts move in various ways. See if you can replicate the squeak by pushing down on various parts of the bumper on all sides of the car. It'll help you localize the noise, and help the guys in the shop (if you take it here) diagnose the problem faster.

Brake pads have wear indicators that make noise when the pads are nearly worn out. This noise could be considered chirping. It's worth checking, anyway, since it's a quick-and-inexpensive fix if it is the problem.

I was thinking brake pads, but its not only when braking, its whenever the cars moving

The wear indicators generally squeak when the brakes are not applied (some stop squeaking when the brakes are applied, some keep squeaking all the time), still might be brakes-- when's the last time you replaced your pads?