Help plz - intermittent vibration in the steering wheel coming from the front

Hi everybody, i've bought a '01 325 Xi last week (it's my winter car, i have a toyota Mr2 turbo as summer car) , i love my bmw, everything work fine except for one thing.

sometimes, the steering wheel shake a lot at 50 mph+ and i can feel that something is wrong on the driver side but i can't find what's wrong. the problem is intermittent, most of the time, i drive the car at 60mph and more and there is no vibration at all but it happened 3 times where the steering wheel began to shake (the same vibration as if the tire is improperly balanced but my tire is perfectly balanced) and every time after a while, the ABS light came on until i stop the car and the vibration never stop until i stop the car too

any idea would be very appreciate

thank you