(Using my friend's Macbook) My friend's MacBook Pro (Unibody) 15" has this problem where the charger makes this small hissing sound when the MacBook Pro is sleeping. (In Windows) It sounds like an oxygen tank slowly losing air or a small sound of the dialup sound. (No signs of problem though when not the MacBook Pro is in use/"awake". What should I do? Will it be a fire hazard?