This article is from the CD-Recordable FAQ, by Andy McFadden (email@example.com) with numerous contributions by others.
Most problems are due to poor digital audio extraction from the source
media. Some CD-ROM drives will return slightly different data every time
an audio track is read. Others, like the Plextor line (e.g. 4Plex, 8Plex,
and 12Plex, but not 6Plex) will return the same data every time so long as
the source media is clean.
The most fundamental problem is that, if the CD is dirty, the error
correction may not be able to correct all of the errors. Some drives will
interpolate the missing samples, some won't.
Another problem some CD-ROM drives face is "jitter". See section (2-15)
See also section (3-3) on avoiding clicks in extracted audio, and section
(5-5) on which CD-ROM drives are recommended.