Does it only do this when there's a disc in the drive? Did you install the drive yourself? Did anything happen right before this started occuring? Have you checked the connections? Have you air-dusted out the drive? (If it's an old drive, it's a good idea to air-dust it, but if it's fairly new, it's not that important, seeing as the dust wouldn't have had sufficient oppurtunity to collect. I once lost a drive to dust, and when it died it exhibited behaviour similar to your drive's current behaviour. That's the reason I'm asking that)
If you can think of anything else pertinent to the issue, let us know, but we need to know at least that much. Post back and let us know.