1. Yip, nothing strange. Happened/happens to my 120 most of the time..bumps and water. Check the bonnet catches first...
2. My e90 335 catches came quite loose after 5000km. (damn...still can't believe) Take to bmw to fix.
3. If you have an aftermarket alarm or early warning netstar system..they sometimes have a switch near the ECU area (bonnet part near windscreen), where the arms close on the switch and can cause it to trigger. Zeemax can also fix it for you, will take Zaid, 5min.