How old, or heavily used, is your burner. This is usually a problem of wear, with alignment, and drive belt.
If your burner has been heavily used it could be worn out after just 7 to 9 months. If it is an HLDS, Sony, or HP and is over a year old, you probably need a new burner.
Suggest Plextor or Yamaha for long life, or LG, Samsung, Pioneer, LiteOn, or NEC among the low priced ones.