Creaking when accelerating or backing up

Creaking is probably just incidental contact between brake rotor and its backing plate (which is often bent when replacing rotors), a small rock stuck temporarily in this gap, or creaking caliper-pad interface. All of the above will probably self-repair. Knocking may indicate loose caliper-bracket mounting bolts...or even a lost bolt that allows the caliper to swing loose and knock a wheel! But you checked that.... Rarely a spring seat will dry out and knock-squeak a bit when starting or braking. Spray a cloud of innocuous lube like WD40 around the lower spring seats and see if it abates.