Buy a lens cleaning CD - use it.

Look at your CDs, allowing the light to reflect off the playing side. Are they scratched? You can get 'scratch fixing kits, but they don;t always work well. Are they dirty? Then look for a cloth or gadget for cleaning them and follow the instructions.

If too badly scratched, or too dirty, you can't fix it. Vibration and jolting may also upset the playback - that's a job for a repairer, or since the cost of fixing and the parts, if available may be prohibitive, then you need a new player.