While you're down there, if the pads look fine, then I would look for something stuck and
rubbing against your rotors.
Grinding noises - the brake pads have worn through and the brake calipers are now
rubbing against the rotors
Not exact matches
Sometimes the rear shield behind the
rotor will get bent and
rub against it.
There is no need for replacing the callipers together, as they will be heavy on your pocket, the reason why the pads and
rotors are replaced together is since they work in tandem and working by
rubbing against each other.