Last night my car made a "whirrring" sound, (if that makes any sense) immediately after starting the car. It lasted about 5 seconds, sounded sort of like a hair dryer under my hood. It did it again last that night, but wouldn't do it again. I was thinking maybe my battery was shorting out and was low and it was my alternator but it didn't do it this morning. So I don't know what to think.