For front loading washing machines, it is recommended to have a full load of laundry. The spinning horizontal axis units may cause added stress to the Magnetic Laundry System, and generate noise. The magnets may not be submerged at this point, but it can also be near the water for it to work.
As an alternative, you can place each of the units inside a durable piece of clothing, such as pants pockets or a pair of thick socks. This will not adversely affect the cleaning action, but to simply soften the landing when the magnets are spinning with your laundry load.