Subaru Impreza 2012 Instruction Manual page 198

Before Using the Audio and Visual System
• Do not attach any ring-shape protector (or other accessory) to the disc.
Although these protectors are commercially available and said to protect
discs and improve sound quality (and anti-vibration effect), in normal use they
can do more harm than good. The most common problems are disc insertion
and ejection problems and abnormal playback problems due to the protector
ring coming off in the disc mechanism.
CD ring
Audio and Visual 197