[HIPPO]

All you can do is make sure the axle is spaced properly, ie the right fork leg flush with the hole in the axle and that the rotors have no runout.

Sometimes fully collapsing each caliper piston a couple of times and pumping it up again helps some.

The OEM pad material seems to be very prone to noise anyway and I prefer to run either Carbon Kevlar or Kevlar pads. Much quieter and have a better initial bite.

 

[HIPPO]

There is no pressure to retract the pistons in to the bores of the caliber. Unlike drum brakes that have springs to pull the shoes away from the drum.

Depends how you phrase it, while there is no pressure to retract the pistons, the drag of the piston seals on the pistons is supposed to deform the seal to some extent and when the pressure is released they will retract the piston when they return to their natural shape. Since they can only develop minimal force this action gets degraded when they lose their elasticity due to wear or overheating or there is even a minimal restriction in fluid return. So, in a way they do have a very short stroke return spring.