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I have a 2020 F150, FX4, 3.5l Ecoboost at about 3500 miles with an intermittent "buzzing" sound from inside the engine compartment. I was washing the truck and started hearing this sound. I appears to be random but the buzzing comes on and goes off, and then there is a long pause before it starts again. The truck is pointed nose-down a few degrees, the parking brake is set, and I had filled the gas tank prior to washing. I've not noticed this when the truck sits on reasonably level ground.
Does this intermittent buzzing have a source/purpose? Do I need to sit in a lawn chair beside the truck and listen for a pattern to "decode" something? I wish I could attach an audio clip but the closest sound that I can associate the noise with is what you hear on TV from the Emergency Broadcast System, only in short bursts,
Just throwing out some possibilities here. Is the cap on your coolant reservoir tight? Does it sound like a vacuum pump? It could also be some kind of on board diagnostic that the truck is running after it turns off. On the equipment that I work on we generally have to install kill switches on them to kill all power. I always advise people to never kill the power to a piece of equipment for at least 5-10 minutes after shutting it down. There is still a few things going on even after you turn the key off.