1999 saab 9-3 problem

I drive a Saab 9-3. In the past few days I've noticed an increase in the sound coming from my engine and slightly less power coming from my car. When i crank the car the engine revs for longer than usual. When I'm driving the loud noise coming from the engine vibrates the whole car, I can feel my seat vibrate when I accelerate. Any ideas what could be wrong?