TomS wrote:
I have a 7D andhad a similar situation photographing a sunrise at the Grand Tetons. It seemed that in low light situations there wasn't enough light for the auto focus to lock on to the subject and kept ranging to find it, which took some time, hence, "busy". When I took it out of auto focus and went to manual focus the problem disappeared...instant shots one after another. At least that's what worked for me. Good luck, and good shooting.