Texases and BustedKnuckles, thanks for the info and the detailed, very helpful explanations!
By the way, if the caliper turned out to be bad, do you suggest to replace both rear calipers or the bad one only? I checked some threads for the issue but the answer is somewhat unclear. If each brand caliper piston has different diameter, both side calipers might need to be replaced together in order to apply the same amount of force to pads. But I have no idea about whether there are common auto brake standards.