2000 Ford winstar

Based on your dandy observations, I would expect to find a loose brake pad that is rattling, or an anti-rattle spring is rusted or broken off. Rattling brake pads are irritating but not generally a safety problem. An inspection would still be a good idea because in rare instances the lining can rust off of the backing plate. Usually the linings can't fall out but it will start to break up over time and if it falls out in pieces, the rotor will be damaged from grinding metal-on-metal. That will add to the expense of the repair. If all that's needed is new anti-rattle hardware, that is available in a kit from the auto parts stores.