A high-pitched squeal is common with high quality brake pads but there are a number of things that can be done to reduce their tendency to squeal. If the noise gets worse in humid weather, and it goes away when the brakes get hot, as in prolonged city driving, there's little that can be done to get rid of it completely. The biggest thing is to bevel the edges of the linings if they didn't come that way already. That removes the "fingernails-on-the-blackboard" effect. Many mechanics don't like to do that because it reduces the squeegee action after driving through deep water. That can lead to loss of braking in severe cases until the water runs out.