Get a CD/DVD drive cleaning kit that uses a wet method. Your local big box computer/office supply stores should have them. Get a good brand like 3M (Imation), Fuji, Maxell or Diskwasher. I disassemble my drives and use chamois or foam swabs and lens cleaning solution, but that's not practical for most people.
Of course it may have nothing to do with the drive's optical system. Let's hope that's all it is...
.bh.