Lately, on occasion, shortly after startup in the morning, my 07 LBZ will start making a low pitched humming sound. Kinda like when the load leveler air compresor kicks in on the wife's Caddy. Hard to tell exactly where it's coming from, but seems like it's behind me around where the fuel tank is. Could this be the fuel pump? I haven't had the truck long and never heard any such noise on my LLY.
Anyone have any guesses??

there is a possibility your truck has a lift pump. crawl under neath there and take a look. if no lift pump, start it, crawl under where you assume the noise is coming from and listen around. did you buy the truck modded or do it yourself? i would be willing to bet if you bought it modded you may have a lift pump