I have noticed the same noise as some of you describe on three different Fords - an 01 F150 w/ 5.4L, an 04 F150 w/ 5.4L, and an 05 Monterey Minivan w/ 4.2L (sorry it's not a truck but this is the one that got the problem solved!) All three have the exact same symptoms - the weather has to be cold, and the high pitched whine happens at at least 2 different very narrow rpm ranges, regardless of engine load. The van had at least 4 distinct rpms. No matter what rpm it occurs at, the pitch of the whine is the same. I bought the van new, so brought it back under warranty. It took return visits over 3 winters to get it resolved, but the dealership was persistent, consulted Ford engineers more than once, and when they finally replaced the alternator, the noise quit for good. That was three years ago. They weren't able to tell me what exactly the problem was. It is interesting that some of you have had success with bearing replacement. I would expect bearing noise to be directly related to rpm, thus have a different frequency for each speed at which it occurs. It could also be brush noise, which would be high-pitched. It must be some fractional multiple of pulley rpm, as the different speeds at which it occurs are too close together to be integer multiples. If I had the time, I would try to solve it on the 04, but it isn't as bad, so I just try to stay away from the speeds that cause it.
You'd think that Ford would have issued a TSB on it by now, since it seems to be prevalent. Maybe one of you has a good connection to a Ford service person who can get a good explanation.

 

I have both a 03 and 04 expedition with 5.4, they both have had the noise since new when it's cold outside. Usually right around 1750 rpm, sounds like a jet goes away as soon as the engine warms up. Dealer worked on the 03 when it was new to no avail. doesn't really bother me and has made it over 100,000 miles now so I'm not real worried about it.

 

My Navi did it again! (see reply #8 above). This time it was light out and I popped the hood while it was "moaning" and the noise is definetly coming from the square box between the MAF and the throttle body. It vibrates like a son-of-a-gun! Put my hand on the box and it feels like a vibrating sander.

Put my hand on the MAF. It is not vibrating. Put my hand on the throttle body. It is not vibrating. Noise is not coming from the serpentine belt or the alternator. If I put my hand on that square intake box it is shaking like crazy. If I blip the throttle the noise goes away and the box stops vibrating at the same instant the noise stops.

I'm gonna have to take the intake tract apart and see if I can see inside that square box. IIRC, the Ford Contour boys talk about the V-6 Contours making a "moosing call". Maybe thats what this is, except it never stops to inhale. I think the Contours boys did something to change the length of the intake tract so as to mess up the harmonics and stop the "moosing call".

If I figure anything out I'll post back what I find . . . .

 

2005 expy engine whine noise only in cold weather. Every year for 8 years. Noise comes a nd goes around 1700-2000 rpm...sitting in park, or at any road speed. 5.4L V8. It sounds like high pitched airflow issue, but the range of rpm and the sound are very tight. Go above or below the range, sound stops. Its the alternator!! Had to have mine changed. Sound went away immediately. Quiet now, no noise at any rpm or speed. This was not an electrical whine (like thru the radio)...it was a mechanical noise. .

 

I hear the "squeal" under load at high RPM, backs off when backing off throttle or making the top of a climb. Could this be the smog pump, charcoal canister or some reed valve issue? I hate when things don't break all the way. 😖

 

Belt slippage.

 

I was having the same high pitched squeal issue from my 2002 Ford Expedition XLT... I however wanted to share something I noticed before the "check engine" light and annoying noise in case it saves someone time so they could do the repair when the temperature is 80degrees instead of negative20degrees

So last summer I was noticing this weird intensity shift when my AC was on... it would be humming along hummmmmmmmm then all of a sudden HUMMMMMMM then back to hummmmm. This was particularly an issue when in park or in traffic (I thought that was the only time, but my truck is very loud so it was just harder when it was moving to tell too). I was worried my compressor was going out, so after a couple months, I took it in. No one could find an issue. So I kept on going. But I have OCD (actual OCD, not just the kind of thing folks say when they are annoyed) so it was really bothering me to have it hummmmmmUMMMMMMMMMummmmmmmUMMMMMMMMMummmmmmmmUMMMM MMMing. So I took it in again and they said the only thing noticeable was a cracked belt. I was a bit skeptical because I had replaced it recently enough that I didn't think there should have been an issue and because my mechanic moved shops and this one seemed really gross and run down, but was like whatever and moved on. But still the noise!!! So I made my guy look at it (not just his co-workers) and he said he really couldn't notice anything and that the air was blowing cold and strong... which by then it was time to start switching from AC to heat anyway... so I decided to wait til next year to deal with my compressor (which is what I thought was starting to go out). So I gave up for then (I often feel things before he can find them... for instance when things are out of alignment). And fall started getting cold (then warm then cold then hot then cool lol). Then I started noticing the issue even with the heat on (instead of the AC) and I was more annoyed... And it got worse when in park. Then it was consistently cold and I thought I had noticed the RPMs being higher than I wanted, but it is old and has a lot wrong with it so I kept letting it be. Then it started being even more noticeable in park that when the louder/more intense HUMMMMMM came the RPMs would go down just a bit, then back up when the hummmmmmmm came back. I thought this was weird, but I was getting ready to be gone teaching in another state for a month without my truck so I let it go. Then I came back and it was wayyyy worse. Then I got a flat tire when it was negative40degrees (and decided I shouldn't put more than 2plugs in my 4th tire and just put on the spare)... then the next day the check engine light came on. Then it started screaming!! And I was like oh something is definitely slipping, but I am broke so I'll deal in a bit. Then it got louder and for longer (since traffic doesn't get fast when the roads are covered in slush and the sides are encroaching on impassable because of the 5ft walls of ice). Then it was running real rough and I was like, I'mma take that in in the morning even though it is something I can check for myself because it is super cold and I am done with winter (or at least the polar vortexes and giant ice melts and collection of ice/snow causing there to be road restrictions in your City called til April 1st) :P

So moral of the story, if you notice hummmmmHUMMMMMMMhummmmmmmmmmmmHUMMMMMMMhummmmmmmmm HUMMMMMMM and RPMs going down during the louder ones while idling and it is nice out, fix it then Don't procrastinate--Check those pulleys and your alternator before you replace multiple belts or send it to the shop multiple times or make everyone in traffic hate you and before you know it you are broke and cold, Sincerely Minnesota-Bound Regret

 

I have the exact same problem here.

Replaced all pulleys and it's still there. Only at around 1700rpms and when cold.

So replacing the alternator bearings did the trick for most of you guys? Where did you find them?

 

Get a rebuild kit, it comes with the bearings and new brushes. You'll get another 100K+ miles out of it.