In 1992, the Audio Home Recording Act created a new fund called the Digital Audio Recording Technologies Fund (DART). This fund is to be shared by writers, publishers, recording artists, and labels. These finds are paid by manufacturers of digital audio recording equipment and recording media, such as blank CDs and personal audio devices, media centers, satellite radio devices, and car audio systems that have recording capabilities.
You should opt in to DART royalties if asked by your PRO at any point. Although thry are not readily available, opting in allows them to be collected by your PRO in the case that they are distributed. You can choose "No" if you would like to make those claims yourself, however.
You can learn more about the Audio Home Recording Act here!