A squealing belt is an indication of improper belt pressure, a misaligned or worn pulley, a worn belt or a sluggish idler roller bearing. Since most late-model autos use a spring-loaded self-tensioning mechanism, examine that first. Attach a socket or ratchet to the tensioner and rotate it. It should flip easily and return to its authentic position on its own. If you’re feeling any binding or have to manually transfer it back into position, replace it.