So I've had this squealing drive belt for a while ,comes & goes! Been using belt dressing to quite it down,finally dressing the problem! I had changed to a GM 12 SI alternator a few years ago & had to modify the brackets. I suspect the alternator pulley not to be in line with the crack pulley,so I moved it rearward a little & lengthen the upper support bracket so can put more tension on it! Should finish this up today,& will see if problem gone!!!