Does it play DVDs OK?
Is this happening with different CDs?
How old is the unit please?
Have you tried a laser lens cleaner?you need a quality one however , seems like there is a contaminated lens for the laser, let me know
Trevor how old is the unit please?
How often is it used for both formats?cd dvd
Trevor its likely the laser pen is on its way out the laser becomes weaker so has trouble tracking in most cases its not an option to replace the laser (depends if the unit is very high spec and expensive) due to the costs.
I am sorry for poor news here
Let me know if you need more help