CD tries to start in sleep mode


Hello, Iam having a issue with my iMac. I put my iMac is sleep mode when I am done and I have had the CD just start trying to work with no CD in the drive. I have got it to quit and come out of sleep mode twice by putting a blank CD in and then it ejects it when it comes out of the sleep. It happened today and the CD trick did not work I had to unplug the computer and eject it after the computer came up. Any suggestions why it is doing that. I have all the current firmware and updates. Running OSX 10.5.5. Thanks