I still think that one of the critical first steps is to flip over the plate and inspect the rim/edge of the mounting screw holes. Even with some brass bridges I've found there to be like parts of a tiny machined ledge, maybe just a few thousandths thick. And I think it gets further exacerbated when some holes have it, and others don't. I actually fixed three genuine Fender plates fairly recently, by removing these tiny burrs. Two of them are on Teles that now exhibit zero squeal, even when I stomp on a Rat pedal. ...I did get a modern plate a couple of years ago - either Kluson or Gotoh. It's a 4 screw but has 6 stainless saddles. The underside of that plate is machined perfectly. I have that one on an Esquire parts build, with a cheap GFS body. It also has zero squeal, even with overdrive and lots of volume. You can actually just pass your fingers under the mounting holes, and see if you feel any burrs. If you do, I suggest removing them.