I have a a 2003 v6 mustang, I was sitting in my drive way witht he AC running an med loading some cds when i hear a popping noises and i think it sounds like a belt popping then i hear a flapping noises, so i pop the hood and from the radiator fan area i can hear the flapping noise, so i turn the car off and the ac turn it back on without the AC running and i see the fan isn't turning and i hear no noises so i turn the ac on the fan starts and i hear the flapping noise again what could this be?

 

sounds like the fan is touching something. make sure nothings got in its way, and that the fan and shroud havent moved, nuts are tight etc.
spin the blade by hand (engine off) and see if you can reproduce the sound and track it down.
god luck

 

We checked for obstructions and there are none and it is only noisy when the fan is turning could this be the fan clutch??

 

Hi,
Can you please post how you fixed your issue ? I am having a similar problem with car overheating and fan rattling.