Dragging cans

A used 7.25 rear-end usually goes for $100 here. I bought a spare. Bad differential gears usually make a high-pitched whining sound. More likely the bearings will make noticeable sounds. I used to be able to take an axle to an auto parts and they would change the bearing (requires cutting off a metal collar and pressing on a new one). But, that was decades ago and those shops are getting rare. But, the tin can sound you describes sounds more like something rattling against the brake backing plate, probably brake components like a self-adjuster that came off.