Why is there a whistling noise when ac, heat or defrost fan is turned past 3? This happens when car is in park or in motion.

What is your question?

Just purchased a used Certified 2017 Ford Escape SE AWD with 27000 miles. The fan makes a high pitch whistling sound when fan is past 3 speed. This happens when in defrost, ac or heat is turned on, whether the car is in motion or in park. Purchased the car with the understanding that Ford Dealer would fix the whistle. Picked up the car after 3 days and was told the technician could not hear it. Turned the car on in the parking lot with the sales rep and we could both still hear the sound. Sales rep brought the technician out and I showed him when it whistles. The car is still at the Ford dealer. I don't think they have a clue or they don't want to fix the issue.

What makes this problem better or worse?

Low fan speed