I was washing my 525 this weekend and as I leaned across the hood I heard the same noise that I was having the problem with. As I pushed down on the edge of the hood by the windshield I could reproduce the noise. So I went to my "test track" and unlached the hood and drove slowly. Voila no noise!!! It seem like when the car goes slowly over bumps and uneven pavement the body flexes and makes the hood flex as well and thus the noise. Now how BMW will fix this is another question. I think I might adjust the rubber nobs under the hood and see if that helps, but the car is going in Tuesday. I hope this helps maybe someone else. I never thought it was the door seals because it just didn't seem like it was coming from that area. Now it is time to go back and enjoy the car.