Humming/Buzzing sounds from under hood

Have a new sound coming from under the hood of 2003 F150. Best way I can describe it is a buzzing/humming sound, similar to almost the way an RC Drone sounds, but a little deeper. It is there idling, in park, drive, reverse. Does not get any louder or quieter with any change, just eventually gets drowned out by road noise. Started last week after nailing a pot hole.

Family mechanic said it was just the “normal power steering whine” but I’ve heard the power steering whine before, and this is a brand new sound the truck has never made before.

5.4L XLT, V8, 4x4, 329,000km (204,xxx miles)

Any ideas as to what it could be before I maybe get a second opinion on it? Thanks!

if it does not change with engine rpm, the only thing I can think off is maybe a heat Sheild got loose and is vibrating.

The Idle Air control valve can make that noise.

Tester

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Hey, I swear I have heard this too. Except I have heard it when the engine is off. Sounds like a Humm or a fan comparable to an electronic device with lots of amperage where you can hear it. I couldn’t locate the exact location, but inside the cab, near the radio and under the hood it sounded center near the firewall where the radio is.

That’s pretty much exactly the same sound and (suspected) location, but never heard it with engine off.

Yup, I swore it was a radio fan or something, but took the fuse out and it still made the noise. It’s an occasional thing.

I think there are a lot of noises we miss because of tire noise or the radio on.

I have read where others have had this problem and it turned out to be the flasher/turn signal relay was defective. but as far as it happening when the vehicle is off, the multifunction relay stays energized for about 30 seconds or so when you shut the vehicle off. I am not sure if either one is the problem, just what I have read so I am passing it on.