My 2001 explorer was great when I first bought it but after a couple of months driving it, it became very loud. There is this loud humming sound when I go above 5 miles an hour and on the highway it gets worse. I can hear it decreasing a bit when I take an exit off the highway and have to reduce speed. It also hesitates at 60 mph. I have come to learn that there are no grease fittings either. So every slight bump I go over you can hear the rubber hitting the metal. It is the most annoying sound. It is loud enough to hear because I have had people actually turn their heads and look at my vehicle when it happens. Does anyone have any suggestions? Thank you.