2005 freestar rear ac has this intermittent squeal. I changed out the blower motor with one from the junk yard, but did not make a difference.

What other Parts back there that could squeal? Sometimes the squealing stops when changing the fan speed. Is there a mini compressor back there?

Going on vacation and would like to fix before the drive...

 

The only compressor in the van is the A/C compressor under the hood. I would take the side panel off and run the A/C. Put the fan position to a speed that generates the noise and start tracking it down. Does it make the noise with the A/C compressor engaged or also when not engaged? Could be airflow thru the rear duct work.