If you are hearing a constant grinding sound- but the brakes are not actually dragging- the first thing to check, is to see if the wear indicators built into the brake pads are rubbing the rotor. This is a warning to prevent you from continuing to drive w/the pads too worn.
If you DO continue to drive, and providing this is the 'problem', the pads WILL destroy the rotors.
If the brakes ARE truly rubbing, they will overheat and smell as well as basically quit working from excessive heat/fade in a relatively short period of time.
In ANY event, it is time to look at the whole brake system- or have them looked at- before you tear up expensive parts or kill someone.