I have an 1986 2WD F250 5.0 EFI. The truck runs, drives and idles amazing. However, when I go to use the rear tank I can hear something humming. I assume its the fuel pump? It sounds like when the power steering pump is low on fluid (which I checked to make sure it wasnt that). The noise goes away when i use the front tank. Any ideas are greatly appreciated. Thanks in advance!!