i ahve a 2012 retina macbook 15". ever since i updated to mavricks i thoguht the sleep mode went quicker i.e. display immediately shuts off. then i realized one quiet morning when i hit sleep the fans were still going...and going...and going for like half a minute before they shut off. the display instantly shut off but obviously if the fans are running th computer hasnt actualyl went to sleep yet. is this normal?