Thank you guys! I had the car checked second time at BMW service. They lifted the car up and inspected the underbody but found nothing unusual. They took the car to the road again to reproduce the sound but unable to make it (yes again it's difficult to run at 100km/h in the city). The technician said that the most potential cause is the tyre, as they said that my rim and wheel bearing should be fine.
I've replaced 2 front tires 2 months ago (goodyear efficient grip Runflat). The 2 rear tires had 34.000km on it. Not sure if runflat that run for more than 30K would cause this weird noise
