It only makes the noise when the engine is on. You can only hear it when standing outside by the back end (not while your in the cab or driving). Also, you can hear it when you're filling the gas tank. It's almost like the hum you hear the ignition when the key is in it and the door is standing open. We just bought so we don't know if it's recently gotten louder or not. Dealer says it's fuel pump and is normal but does it mean the pump is going bad? It runs great and idles great. Just a noise.