I finally found out what the loud humming was. It was the power steering. My was low as hell. It didn't even show up on the dipstick. I filled it up and humming is gone. By the way, the 300C power steering uses transmission fluid. I had to ask the guy in Murry's 3 times was he sure, then I read the book and its true. No more humming. I am still going to make an appointment at my dealership just in case. Everyone check your fluid levels. The guy at Murry's said I must had a leak because it sould not be low already, while my father says that they just my not have filled it up.