Is this a vacuum leak?
 

So this is starting to bug me, so I thought I would ask here.

1. This is a slight whistling sound. Not a grinding or squeaking sound. Which leads me to believe it is not the Alternator or any pulleys.

2. It kinda cuts in and out. It is not a steady sound. Kind of like "whistle whistle quiet whistle whistle quiet quiet quiet whistle"

3. It sounds as though it is coming from the Engine Compartment.

4. It only makes this sound at low speeds while driving. <20mph. Does not make the sound with the Engine in park, sitting still (one of the reasons I can't figure it out)

5. It is most noticeable when I drive my truck for the first time on any given day, or after the truck has been sitting a while.

6. I have looked around and have not found any broken, cracked, missing hoses.

7. The noise is steady, it does not get louder or quieter depending on how mush I press the accelerator.

8. It almost sounds like air escaping from somewhere.

Well any advice would be great. I can't figure this out and I don't want to go and just change a bunch of parts trying to sort this out.

Thanks!!:thumbup::thumbup::thumbup::thumbup:

1. Check to see if 4x4 works
2. Make sure you aren't missing the foam gasket around the air filter housing https://www.f150forum.com/f4/bog-dow...solved-166431/
3. Pull the air tunnel out of the fender to check for leaves and crap.

Checking those really quieted down my ride in the past. Hope it helps!

Alright , good call, Ill go check :)

So I checked all of that.

4x4 is working.
Replaced that gasket around the Air Filter (and the Air Filter)
Took the Air Tunnel off and cleaned it out.

Runs better, that's for sure, but the sound is still there..

I did notice this just now though. It is hard to see but the little hose inside the red box has nothing plugged into it...Could that be the culprit? I don't feel any suction or anything from the hose with the engine running (but I obviously can't check it while I am driving, when it makes the noise)
https://cimg9.ibsrv.net/gimg/www.f15...944c23f09a.jpg

That's the vent for the drivers side IWE. Supposed to be dangling like that.
Hopefully someone else will chime in too. I may be out of ideas lol

Is this a vacuum leak?
 

Have you checked the windshield trim? When I first bought my truck, it had a whistle and later a rattle that turned out to be a broken clip on the trim running up the driver side. I also remember reading about a few guys that had aftermarket grills that would whistle at certain speeds.

I also have the same issue with my 2012 stx . I have checked everything from the passenger side pcv valve and hose ( which leaked, and after fixing I still had the whistle ) all the way over to the check valve that's on the vacuum line before the brake booster ( which leaked very little) but I siliconed that and it's still whistling on acceleration which leads me to believe it's related to the actuators on the 4 wheel drive . Try driving it in 4 wheel drive and if the whistle stops it's somewhere in the vacuum lines that go to the iwe's . . Hope this helps

Checked the trim, Didn't see any leaks.

It still makes the noise while driving in 4wd.

I have fingerf*cked just about every hose/valve/anything I can find under the hood.

I guess I will try replacing the PVC valve and see how that goes. But I kinda doubt it's going to do the trick..

Is there maybe something on the transmission I should check? I checked the vent hose (as much of it as I could without yanking off parts to get to the rest) and it seemed ok..

Is this a vacuum leak?
 

That may be a little difficult, as the PCV valve is part of the valve cover and cannot be replaced separately.

Yah I saw that today. Big nevermind on that. Probably not the problem any ways.