i was dropping off my grandfather at a relatives house when my x5 shut down turned off. i tried to start it but got a weird buzzing sound under the hood. after 3 tries it started again and i was able to get the car to the mechanic. there are times when i start it and get no noise and other times i do. it's a pretty loud vibration buzzing sound under the hood and i have no clue what is going on . please help.