1994 F150 2WD Gasoline Engine, in great shape runs like new (photo attached). I am getting a medium pitched hum from the engine compartment. It is intermediate but I am now hearing it about 90 % of the time. I went to the dealer and they said that they thought it was the power steering pump however I hear the hum whether or not I am turning the wheel. I really don’t how to describe except as a hum. It sounds just like a hum as if you were humming with your mouth closed. It is a constant pitch and sound level (loudness). It is not the “normal” whine power steering sound. The dealer said it could possibly be a bearing in the power steering pump but was not 100% sure.
I elected not to replace the power steering pump until I had a more definitive answer. It disappears after I go above 20 MPH, I am not sure if this is due to road noise or the hum just disappears. I think it just disappears above 20 MPH. Anytime I am less than 20 MPH (moving or idling.) I can hear the hum. Can anyone help me?

https://www.f150online.com/galleries/...cfm?gnum=11729

 

how knobby are your tires? and ford power steering pumps are always loud ha.

 

I had a similar problem once, turned out to be corrosion on the coil wire!

 

which side of the engine is it coming from?

 

use a long screw driver like a stethoscope, touch the pointy end on the pump and the handle on your ear and listen to a bunch of stuff until you hear which part it is. BE CAREFUL!! putting the pointy end in turning belts and pullies can be dangerous. Maybe you can hear it.

 

Does it change with RPM? My '88 was doing something similar turned out the bearings in the water pump were bad. Grab the fan and see if you can wiggle it. ( Engine OFF obviously!)