On the back of the blank CD-R packaging it says to write on the gold (nonrecording) side with a permanent felt-tip marker. If a 'Sharpie' is used it could ruin the CD! Apparently the Sharpie has a hard enough core to scratch the metal backing. If you look on the green (recording) side, you can see a metallic image of the writing on the other side. Only a little, but enough to cause the clicking.