2003 Ford Crown Victoria Belt squeal

I have a 2003 crown Victoria police interceptor. The belt squeal is driving me crazy. I replaced the tensioner and the squeal got even louder. I have a new gatorback Goodyear belt coming in as well as a new idler pulley. Mabe that will cure it
mabe not. Also, my brakes have low pedal. Guy before me replaced master cylinder. But brakes still havelow pedal.