1. remove any disk in the CD drive. Does that fix the problem? <<edit: ignore this, you clearly said the drive was empty>>
2. Go into the BIOS. While you are in the BIOS is the CD drive running? If yes then it's probably a bad CD drive as inzone says. Good news -- it's a really cheap part.
3. IF the CD drive does not run while you are sitting in the BIOS but does run when empty when you are in Windows then some piece of software (anti-virus? something you partially installed? ??) is trying to read the drive. Post a reply and we can try to isolate what program is trying to read the drive.