Ford Galaxy engine rotates every time but occasionaly wont start

my engine rotates every time but three times over the last 2 weeks it has failed to start. I try to start the car 3 times, if it doesnt fire i leave it a few minutes then try again and it eventually starts (up to 7 attempts) there didnt appear to be any other problems, the car has been driving fine once started, however today there was a loud high pitch whistling/rattling noise for a few minutes which has now gone again. The few times i have had problems starting up has been after using the car for a few short journeys so the engine has been turned on and off quite a few times in a short space of time but i'm not sure if this is relevant to the problem.