Apple PowerBook (3400 series) - Manual (Page 46)

4 Push the tray in to close it.
Note: When the CD-ROM drive is in use, you may notice some vibration as
the compact disc spins rapidly. Certain discs can cause the drive to vibrate
because they have heavily inked artwork or a label that creates an imbalance
as the drive spins.
Some vibration is not unusual for a high-speed CD-ROM drive. To minimize
vibration from unbalanced compact discs, do not put labels on your CDs.
In addition, place the computer on a flat, solid surface when using the
CD-ROM drive.
Keep the CD-ROM drive’s tray closed except when loading discs. This
prevents dust from getting inside the mechanism. Also be sure to keep CDs
free of dust and grease.
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