Buddy has an 04 1/2 ton Chevy and said he went out to his truck and heard a buzzing noise coming from underneath right at the cab and bed. He thought it was the fuel pump and unhooked the battery and it went away. Hooked the battery back up and same thing. Even w/ the truck not running it still buzzes, but it will start and you can still hear the buzzing noise. Fuel pump or something else, anyone had this issue before?