I hear a loud squeal when I am on a hill waiting in a line to pick my boys up from school.

Each time I move up a car spot while waiting in line I hear this loud squealing sound. When I am going down the hill I do no hear this noise. What gives? It seems as though the car is in pain when going up the hill. Yes, I am only going about 10 miles per hour in line. What could this be?

Matt