under hood buzz

[thewishkah]

Today I was under the truck replacing the running board lights when I noticed with the key on engine off there was a constant buzzing sound coming from under the hood and was loudest behind the drivers wheel well. The best way I could describe the sound was it sounded like a fuel pump priming but was up front and stayed on as long as the key was in the on position. Once I start it I can no longer hear the sound (not sure if it went away or just cant be heard while the engine is running).

I can't say I ever noticed this sound before but its not often I have the key in the on position and the engine off. I do have an ABS light on for the front drivers side sensor and the pump saying it is out of range ( i think?). When I had the code read(I don't have an abs reader) they said most likely when I replace the sensor it should operate just fine that the pump said that cause it tried to apply the abs to often. Could this be the pump buzzing or humming? Just a thought. Any info would be greatly appreciated.

 

[IMINYOURCHAIR]

Mine did/does this too. never investigated it further than you have. I believe it to be something in the transmission

 

[Bedrck47]

One thing you could try is to remove fuses one at a time to find out which circuit is causing the buzzing You would only need to be concerned with the fuses that have power going into them when the key is in the on position

 

[BAD RONALD]

On my '89 Bronco I used to hear a similar noise. The ignition key did not have to be "on".

Turned out that what I was hearing was the starter solenoid energizing. It would happen randomly and was audible to anyone walking past the truck. Apparently this was common in older Fords and was corrected with a replacement solenoid. According to the old timer who pointed this out, it was near as common to have a truck with a failing solenoid engage the starter, turning over and over trying to self start.