pop your hood and take a look at your serpentine belt.... take a look at a spot where you can see the bottom side of the belt wrapped around a pully (engine should not be running) if there is cracking there... its time to replace the belt... I am willing to bet that is your stock serp. belt with 78K miles. Get a goodyear gatorback belt... when you hit higher RPM's they tend to whine and sound like a supercharger
