Very loud screeching when the car is started and AC is turned on?

What is your question?

Whenever I start the car after it has sat for greater than 15 minutes and either the AC is already on or I turn it on there is an extremely loud screeching noise that stops when I turn the blower off. It will eventually stop screeching after I use the AC for a few minutes. I had this checked while I was getting an oil change and the ran the car just like I told them and the whole place stopped what they were doing (a 6 bay Firestone). The technician told me to have the dealer check it out but to this day they can't get it to happen. Once when I picked it up from them the screeching happened right next to an open bay and no one inside heard it but all the patrons on the sales floor and outside covered their ears. It is so loud that my passengers have covered their ears even with the windows closed. Any ideas?