1997 Ford F-150 Squeaking under the hood

For some time now, when I turn the steering wheel a fairly loud squeal emanates from the front end of the vehicle. The squeal sounded like maybe some sort of pushrod was moving through a rubber seal without lubrication.

I got under the truck and looked for such a situation and found nothing like that. There are only a few grease fittings on the steering linkages which I made sure were well lubed. I also sprayed penetrating lube on just about every movable part of the steering and front suspension. Still the squeal was present.

Though the squeal is fairly loud, I do not hear it when I am driving with the windows up. The only time I heard it was when the windows were down and there was something around to reflect sound back at me like at a drive-thru window or inside a parking garage. Incidentally, in areas such as this the steering inputs are fairly large in magnitude compared with driving down the road.

More recently I have noticed small intermittent squeaks coming from under the hood when it is parked and idling. These squeaks sound similar to the big one, just shorter in duration and less loud.

I am wondering if the the problem might be related to the power steering pump. My theory is that the pump is squealing a little while idling, and a lot more when placed under load as turning the steering wheel hard over would do.

Incidentally, the serpentine belt was replaced a few years ago so it likely is not the source of the problem.