Reviving an older thread here.....

I have this issue with my truck, however it's not just in cold weather, it's year round.

About 1800-1900 rpm I get a whistle under the hood, in cold weather it's very high pitched, in warm weather it's more of a drone.

Here's the kicker, when I run cruise control, the noise goes away.

Anyone got any ideas?:confused:

Any chance this could be a IAC valve problem?

No, because you don't have an IAC, you have an electronic throttle.

Right, drive by wire...... oops.:lol:

Gentlemen,

I have 04, f150 Same issues (4.6L). I am almost positive its the alternator. Like other have said happens when about 0 degs out or colder, lasts about 10 seconds. It will last a little longer if its really cold(up to 30 seconds).

Now the second issue the one at 1800-1900 rpm range i have as well. I believe its feedback from the alternator into the electrical system through the speakers. They have special diodes that prevent this from happening and cause increased ripple voltage(if they fail). The part that does not make sense is this rpm noise feedback only happens when its cold in the winter which may bust my diode failure theory. I swear the noise comes through the speakers not the engine bay. (different that the noise at initial startup when cold)

This weekend im going to swap out my belt and while its off going to give my alternator a spin and check things out. (I will replace my alternator if i hear slight grinding or odd bearing noise).

Side note for the worse mileage in winter issue. In addition to the reasons stated above, when its cold the transmission delays shifting into overdrive too keep the RPMS up to heat up the tranny (fluid friction in the torque converter) this decreases mileage. Happens every winter to me.

I'll follow up next week on the status though its not cold enough to officially confirm this fix yet.

Later,

i have a 08 f150 with a 5.4 had the same problem it was a 6l3z 6c348 pully,,,recall on 08 replaced it at n/c

My truck has experienced the annoying cold weather high pitched whistle since new. I can't go another winter listening to this whistle and just ordered an alternator and new belt. Going to throw on a new fan clutch as well. Hopefully, I will catch the culprit with these changes!

i have an 04 that up until thursday did the same thing. Replaced the alternator with a genuine Ford Reman Alt at the dealership i work at and have since driven it approx 200 miles without a sound. Hope it helps guys

LOL, I'm 5 years late to the party. I've had this noise since the truck was new 5 years ago. My magic temp used to be 7 degrees, now it's up to 20 so it's been doing it more lately it seems.

An audio of the exact sound (from another guys truck) is posted at #166 in this thread.
https://www.f150online.com/forums/3543175-post166.html

The TSB link and fix for this problem is located at post #180
https://www.f150online.com/forums/3557647-post180.html


It seems now that anyone with any type of whine, whistle, whoot, or noise is posting in this thread.

Paul

Problem solved !

I have had it in very cold weather since I bought the truck new and just the other day it happened again. My radio was on and I just reached over and pushed the knob off to listen better. When the radio went off so did the whistle at the exact same time. So like someone stated above I believe it is some type of altenator whine and it comes through the speakers.

My '06 4.6 makes the same noise, only when cold (teens and 20s F). Noise is the same with the radio off-it's in the engine bay. It's intermittant and never lasts more than a few minutes. No big deal.

If yours whines through the speakers, you may have a ground-loop issue. Personally, mine whines when it's below 15* and only between 45-55 mph. Once is does whine, it last 2 mins tops - then stops.

Mine makes the whining noise when it's 12* or less around 1600 RPM's (55 mph) If I go to 60+ mph it goes away and it sounds like it's coming from the TB.

I had a whistle from the engine compartment when temps were below 15*. I replaced the alternator last week and the noise is gone.

O2 sensor! Happened to me in '99 on my '98 F150 Eddy Bauer and again now on my '05 F150 Lariat! Something about crystalizing going on in very cold weather causing a whistle as the air crosses the sensor. I'm no expert, just what a mechanic told me and that fixed the noise problems.