Mine makes the noise on a/c, and defrost only.
Wonder if it's the same problem?

 

What did the dealer whack you for that job?

 

Dealers, God I hate dealerships!

 

Yeah sounds like the blender door to me. The tabs that control the door are cheap plastic and they begin to twist. If one breaks off the door can dangle for a while and flutter inside the blender at high fan speed. Eventually it will break completely and cover the floor heat portion. Because of where the blender door is located, it requires removal of the dash to replace. This is an estimated 9 hour job I believe. They built a faulty part but will not do a recall because of the labor involved to properly repair it. Heater treater has a replacement with a full metal bar across the blender door that completely solves the problem forever. Do a search for blender door and there are a bunch of quick fixes through the glove box. Not a complete and proper repair, but stops the noise.

 

Can someone tell me what is causing that loud humming sound when I turn on my AC/Heater in my 2010 Dodge Caravan and what I neex to know????

 

Look in the fan/ blower motor. I had a similar issue and there was small debris in it. Cleaned it out and got rid of the noise entirely.
Good Luck!