I had that problem in the past using the stock Fender bridge plate, with several different pickups, including a Bill Lawrence noisefree bridge pickup. The Dimarzio Area T was dead quiet, I changed to a Callaham cutaway bridge , much thicker and flatter plate, it also has 2 small screws at the top corners of the bridge plate. Later I used a Fralin Blues, HD Super 90 (great pickup!) and a lot of others and no more squealing. And for the most part I was having issues at moderate volume and gain, blues, R&B, some R&R. So I think it's a combination of bridge plate and the pickup that caused it and some pickups are microphonic which can be accentuated by a stock thin stamped steel bridge plate.