GMC Sierra Denali Classic 2007 Owner's Manual page 222

Playing a CD
Insert a CD partway into the slot, label side up. The
player will pull it in and the CD should begin playing.
If you want to insert a CD with the ignition off, first
press the eject button or the INFO knob.
If the ignition or radio is turned off with the CD in
the player, it will stay in the player. When the
ignition or radio is turned on, the CD will
start playing where it stopped, if it was the last
selected audio source.
When a CD is inserted, the CD symbol will appear
on the display. As each new track starts to play,
the track number will appear on the display.
The CD player can play the smaller 3 inch (8 cm)
single CDs with an adapter ring. Full-size CDs
and the smaller CDs are loaded in the same
manner.
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If playing a CD-R, the sound quality may be
reduced due to CD-R quality, the method of
recording, the quality of the music that has been
recorded, and the way the CD-R has been
handled. There may be an increase in skipping,
difficulty in finding tracks, and/or difficulty in loading
and ejecting. If these problems occur, check the
bottom surface of the CD. If the surface of the CD
is damaged, such as cracked, broken, or
scratched, the CD will not play properly. If the
surface of the CD is soiled, see Care of Your CDs
and DVDs on page 249 for more information.
If there is no apparent damage, try a known
good CD.
Do not add any label to a CD, it could get caught
in the CD player. If a CD is recorded on a
personal computer and a description label is
needed, try labeling the top of the recorded CD
with a marking pen instead.