I've had this problem for some time. First, with Endless SSYs and DBA 4000s the squealing was unbearable. We tried everything - chamfering, machining, goo, shims, Bendix Ultimates...
Anyhow, I had Bendix Heavy Duty put in recently and although better, they still squealed.
Eventually, someone worked out that the seals were worn in the calipers, and when the piston moved towards the rotor, the seal tried to roll with it and thus the piston wouldn't detract properly, leaving the pad contacting the rotor lightly = heat = glaze = squeak etc etc
Long story short, I had all my calipers rebuilt. Seal kits were about $100 each caliper and the same for labour. After this, it was dead silent. That was about a week ago and although I do get some minor, minor squeaks, its 1000 times improved. I'm just hoping it doesn't come back.
Just my 2c...