Engine Noise on Start up

A couple of days ago I noticed a strange noise coming out of the engine bay...sounds like something is grinding on something...like the fan hitting something, but it only last for about 1 min then it's back to normal? I have spend ages trying to find this noise but no luck. When I turn the car off and turn the fan I hear nothing....any comments on this?

Thanks heaps

btw anyone in QLD going to cruiser park this coming weekend