Hi all Ihave been chasing this noise for a couple of month now, I found
this Topic from 2002 today by Mike Mayer, and his description is
Identical to my problem (See below).
Has any one else run into this and found a fix, I was going to start a
tear down of top end until I saw the info about possible bad injector.
does any one know mike and how to get a hold of him to see what he
found to be the source of this anoying sqyeak/chirp.
I was sure it was a rotational squeak until the reference about
injector pulse width.

Issue:

"When the engine is cold, I hear a repeating metallic sqeaking or
chirping
coming from the area of the rear of the engine.  This is the 4.0L V6.
After
about 5-10 min of driving, it goes away.  Sometimes, it's gone even for

several weeks - even when cold.

The chirping goes about 400 - 450 times a minute as the engine is
idling at
about 800-900 RPM.  That tells me the chirping is happening at half
crankshaft speed.   The spark plugs, fuel injectors, and valves all do
their
thing at half the speed of crank rotation, so I suppose any are
suspect.

Using the ear on the wooden-dowel-against-the-engine trick, I hear
nothing
inside like a clattering valve or bearing, and no chirping thru the
dowel.
But can still hear the chirp when just standing there listening.

I listen with the dowel to the injectors and you can clearly hear the
rapid
tic-tic-tic-tic-tic of the injectors (that's normal).  But I don't hear
the
chirp in the dowel, only from the back of the engine without the dowel,
as
if it's external to the engine.   The ticking of the injectors is in
sync to
the chirp repeating, so that verified for me that it's at half crank
speed.
Seems to regular to be a rubbing part on the outside of the engine.

It's not the serpentine belt - we even pulled it off and started the
engine
for a couple second without the belt - and we still hear the chirping.
So
that rules out any of the belt-driven accessories and the idler pulley
and
tensioner, as well ruling out the water pump.

Question is, can a fuel injector squeak?   I can't imagine it's the cam
or
the lifters or the valve guides, as they are all bathed well in oil.
Plenty
of oil per the dipstick, and plenty of oil pressure per the OP guage. "

Thanks for any clues...

Mike