I have a 2006 BMW Li the other day I heard noise coming from under the hood.

Hello, What happened when you tried to start the engine? Did it crank and never start, or just nothing happened? The vehicle will not start if it has detected a damaging failure in some cases, and since coolant is leaking onto the engine somewhere, I would say that is the culprit. This is a built in protection to further damage. The battery most likely went dead from cranking for too long without starting. I recommend bringing this to one of our certified shops for diagnosis, and when you look at the list, make sure to select one that specifies BMW, or has a BMW expert on staff. http://repairpal.com/bmw-within-10-miles-of-rockingham-north-carolina-28379