I'm not trying to hijack this thread but the exact same thing has just happened to my car. 07 plate with 63k on the clock. Strangest thing ever is that in happened on a perfectly normal straight flat road with no bumps or anything. Went from no noise to a horrible knocking noise, I thought one of the bonnet catches had given up and it was the bonnet bouncing up and down. I've owned the car for 2 years and it's never had an accident in that time, obviously don't know what happened to it before but it's been perfect for 2 years. I have no idea how it's broken with such a clean cut, it's exactly the same as the OP and by the looks of it in an identical place. Oh well, I'll give BMW a call and see if it's covered under the warranty?