I have noticed a strange sound like a rattling.

This could be a serious problem if the brake pad is not returning to its poostion as it needs to constantly ride on the rotor so it does not cock sideways and catch and momentarily or abrublty stopp the car. The caliper proabalby needs replacement and you should do it before driving it anymore as it is a critical safety issue. You should also check the caliper itself to make sure the mounting harware is not loose and the claiper is not moving aorund itself.