Q: Why would my passenger side drum brake engage when I'm not touching the brake pedal and then release?

Do any warning lights come on when this happens? If you are having an issue with the ABS system (which is kind of unlikely), or an issue with the brake sensors the vehicle will likely set codes which can be read in a scan.

This could also be from a bad yaw sensor. The yaw sensor detects certain angles of tilt during a turn. If it is calibrated incorrectly, it will cause the brakes to engage to correct the tilt. The yaw sensor will need to be replaced if it is found to be faulty. You will also want to check for any kind of mechanical issues. This would include any loose retaining bolts or guides, rusted out or damaged components, or anything bent or out of shape. If you would like to have a professional inspect the brake system, a certified technician from YourMechanic can come to your car’s location to have this taken care of.