I had the same problem as you, only no buzzing, and i wasnt running a chip. You would turn the key one click, listen for the pump to run, and then start the truck. Well when i did this, the pump didnt run, and it made no noise. So before my dumbass even gave 2 thoughts to check the relay, i dropped the gas tank. And after getting all the gas in it out of it, I had to spend even more time getting it down. So once it was down I replaced the pump, and still didnt work. F***!! So i looked at the relay and it was all corroded, so I sprayed it with some brakes part cleaner, cleaned it up real nice, plugged it back in, and O YES THE EXPO IS BACK. So make sure you check everything before you go thorugh the mess of dropping the gas tank, cause that sucks.