CD noise when sleeping

[dimme]

I have a SR 2.4 Macbook pro. I have had it for about 1.5 years. It is running 10.5 with the latest updates. I never turn off the computer just close the lid when zI am not using it. I noticed in the last two weeks when I do this the cd will make a noise like it is waking up and the apple logo will flash for a half second. This happens every 2 minuets or so. So for now I just shut off the thing. If I chose sleep from the apple menu and leave the case open all is fine.
Anyone have any ideas what is going on?

 

[dimme]

So I now I sleep with the id open and all is fine. I still can't figure out why it will not sleep with lid closed.