Forgot to mention that the PS fluid is still a nice red color and is at
the correct level.

Sounds like pump shaft bearing is going, or possibly the belts aren't
tight enough.

Perhaps, the pulley bolt to shaft isn't tight enough?

Before you do anything, stand outside your vehicle and have someone
else park it in the driveway.  Pay attention to the noise it makes.
Then go hang out in a busy parking lot and wait for another Explorer to
come by.  In fact, listen to ALL the Fords that come through.  I say
this because Fords are notorious for noisy PS pumps.  Yours might just
be making the 'normal' noise.

Part of the noisiness is due to the plastic housing on the pumps, and
there's not a whole lot you can do about that.  (I've often wondered
about blasting my PS pump with some of that rubbery undercoating stuff,
but I don't know what sort of heat issues that might cause).

IIRC, i once read on this ng (or maybe it was alt.trucks.ford) about a
PS fluid (or additive, can't remember which) that Ford developed to
quiet the PS pump.  Never tried it myself, don't know how effective it
is.  I just deal with the noise.

Good luck.

-phaeton

I have had this problem with almost every Ford PS pump I've
owned over the last 25 years.  For the last several, I have
found that flushing and filling with Dexron and adding 2 oz
of Lubegard red will quite them right down to almost dead
silent.  The noise is caused by either cavitation because of
air entrained in the fluid or the relief valve chattering.
I do not know if the Lubegard works by reducing the air
entrained in the fluid or some lubricating ability but, it
has worked on every one I've had over the last 15 years.
There are other similar additives but, I have not used any
of them since I am basically additive resistant in nature.
The synthetic Dexron may work the same way since it probably
has different additives.  I would not replace the pump
before trying the flush and additive - I have replaced
several with negative results.

Lugnut