I just purchased a 2013 F-150 a couple weeks ago. When I was test driving it I noticed the heat/cool fan was extremely loud when turned on and it didn't matter what speed you turned it on. It was so loud you couldn't hear the radio. It seems louder actually when its on the lower speeds Turning it to AC doesn't change the sound. The dealership I bought it from is a Hundyai (?) dealership so their service department is not all that familiar with Fords. They are taking a look at it today but wanted any advise or any one who has had a similiar issue so I can deter any unwanted tinkering with my truck.

 

It might be the bearings in the fan motor. Only way to find out is to get at the motor.