Really loud fan in grill on AC #4 setting?

[FLfinfan]

I noticed today (2nd day with truck) that when the truck had been sitting for awhile shut off, and I started the truck and put the AC on high (#4), the little fan on the lower part of the trucks front grill sounded really loud! It sounded like the truck was a coffe grinder without beans or like it would blow up. You had to open the hood just to hear the motor over the fan. Is this normal? I have heard cooling fans before but NEVER this loud.

When I turned the AC to #3 it turned the fan off after about 2 or 3 minutes. If I repeated the AC to #4 deal the fan started it's really loud fan noise again. This time I turned it down to #2 and the fan stopped much sooner. Did the #4 setting again and when the fan started making it's really loud fan noise I turned it to #1 and it stopped right away almost. When I started the truck on number 1, 2, and 3 settings the fan did not come on. Keep in mind the truck had been sitting, off, for hours, not running.

I have had other cars with the cooling fans before, but never this loud, and they never came on when the truck was cold. My other cars turned on their relatively quiet fans after a significant drive on a hot day. Does anyone have a loud fan on #4 AC setting also. Maybe you northen guys aren't at that temperature yet to use AC much, but I am here in FLA. Input please.