I have a 2001 Buick Century with about 65K miles. The ABS brake light, Check engine light and Trac off light are all on. Just recently the lights haven't been coming on until a few minutes after starting and driving the car. Before they come on there is a noise that sounds like a small electric motor, similar to the windshield wiper fluid pump noise. When I press on the brakes there is a weird vibrating sensation. It feels very unstable and sometimes I wonder if the brakes are going to work. Suddenly the three lights come on and the brakes work just fine. Does anybody know what the problem is?