This has been the rule for me since updating to leopard. If I launch front row and listen to some music at night, when I wake up in the morning my iMac will be frozen and often makes this loud, horrible clicking noise. Needless to say, this scared me because it seemed deadly so I've stopped using it until apple addresses this in 6 months. It is a total freeze up like those that appear to be related to the graphics cards in the new imacs. Other ideas on causes? others experience this?