I've got a new 12" iBook but it is driving me mad. If I run it purely from the battery and then close the lid the machine goes to sleep with no problems and stays absolutely silent. When I lift the lid the machine whirrs back into life with the usual clicks If the AC Power is connected and I close the lid it will not go to sleep. Every few seconds it whirrs and clicks as if I had opened the lid. Yet as soon as I remove the power it falls silent. What is going on? I've reset NVRAM, PMU to no avail. Should the machine be able to sleep with the lid closed when power is attached? HELP!!