What I'm about to ask is probably a normal condition, but I just want to be sure. I have a 2010 F250, 6.4, 4X4 with about 64,000 mi. I tow a travel trailer about 8000 lbs, or so. When I tow over a very steep grade (Cuesta Grade in CA, for example), it seems like there is a very loud "fan" noise...
