What other causes for Squealing Belts in car with new high-end belts?

check for belt tightness.. there should be no more that a half inch play in it ( push down on belt and see how it goes down) possibility is your friend put on the wrong type of belt one thing that might help is go to your local auto part store and ask for their advice and you can either buy a repair manual for you car for how to do it your self or they might be able to print you up a copy of instructions on how to do it also