Ever since manufacturers had to go from asbestos to semi-metallic pads, squeal has been more of a problem (metal -to-metal contact, DUH).
I had a mechanic friend of mine that would cure the problem by making cross-hatched cuts across the pads. Might be worth a try...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car