Every now and again my Macbook will wake with the lid closed. For Example Last night I closed the lid, Macbook sleeps. About 20 minutes later the apple logo turns on for a few seconds, then off for about 15 seconds, then back on for a few and it sounds like it accesses the Superdrive, which is empty, then it goes off. This has happened several times. So I went through my power settings and turned off Wake by Network which is on by default. Is there anything else I should look for?