The first step to troubleshooting almost any BS9000 weird behavior is to clean any dust from the hand sensors - these are 2 small clear posts that stick out near the top of the metal deck (the metal surrounding the CD holes) to the left and right of the cd 1 and cd 6 holes. When clean, these sense obstructions to the CD carriage path so that it doesn't wack your hand at high speeds. When dirty, they can cause all kinds of weird things to happen.
If this doesn't work, then there's always the hard reset (unplug for ~ 1 minute).
After that, it usually requires a professional... or the help of professionals on this board (not me).
Stan