Not all CDs and DVDs are created alike. Some discs may be slightly thicker than others, some may have labels affixed to their tops, and others may have scratches or other defects on the playing surface. Any of these things can cause your computer's optical drive to make unexpected noise (such as constant grinding) when you insert the disc. To find the cause of your issue, try this:
1 Make sure that the disc is fully seated in the optical drive tray (this doesn't apply to computer models with slot-loading drives).
2 Eject the disc and examine its surface. If there are any fingerprints, dust, or dirt, wipe the disc with a dry, lint-free cloth and try it again. If the disc has major scratches, do not use it.
3 If you still hear noise, eject the disc and insert another. If the noise goes away, the disc is the likely culprit (you may want to contact the manufacturer for a replacement). If you still hear noise, try another type of disc (for example, if you inserted an audio CD, try a DVD movie disc or a CD that contains data files).
4 If you still hear noise, your computer may need service. Contact your Apple Service Provider.