Yes, some differentials may have magnets installed in them. The purpose of these magnets is to attract and trap any metal particles that may be found in the differential oil. These particles can damage the differential components over time, so the magnets help to prevent this from happening. The magnets are typically located either in the differential case or in the drain plug of the differential. It is a good practice to inspect and clean these magnets during routine differential oil changes. If there are no magnets present in your differential, it may be possible to install aftermarket magnets to help protect your differential components.