Since I got my ranger I have noticed a loud whinning/buzzing noise from underneath. At first I figured it was an exhaust leak but today I checked and everything is fine. So then i get my ear right under the truck while it is running. I found that the noise seems to be coming from the fuel tank. Its an ear pearcing sounds when you get within a 6 or 7 inches of the tank. It makes this sounds only when the truck is running and the tone never changes. Any ideas of what kind of problem I have to deal with???