Been out of the country for a few weeks, came home and had rotator cuff surgery right away so I have not driven my '06 FX4 for several weeks, it was washed and put away before I left.
Took it to get gas today and heard one hell of a noise, almost a whine/rubbing against sheetmetal type that got louder the faster I drove. When I flipped the 4x4 switch the noise goes away most of the time, however it did return one time while the light said it was engaged, however I have my doubt if it was engaged.
Unfortunately I can not climb under it for several more weeks as I have no use of my left arm and am all slinged up.
Could this be the IWE selonoid? Its not a brake hanging up as I checked for that.

 

Might want to take a look-see as best you can (I know you're gimped up) at the vac lines, could have been rodent chewed while it was parked. They need to have vac to keep it out of 4WD the way I understand it.

 

It could be the solenoid, only because you said the noise also happened while in 4x4. I don't know about the noise getting louder as you go faster though. When you let off the gas does it go away? Should get the new solenoid(with the cover) either way... I wish I would have gotten mine earlier and would have probably saved me a few hundred dollars. You can probably even change it with one hand!

 

Here is something easy to do, start the truck (make sure the truck is in park and emgerency brake is on) dont want to get in a lawsuit. Then have someone climb under there and see if they can spin the axle shafts on both sides. They should spin some what freely bc the IWEs arent engaged while the truck is running (not unless the truck is in 4wd) which then the vacuum is no longer applied to the IWEs.

 

here are a couple threads that might help you. i just replaced my drivers side IWE actuator and the vacuum lines that go to the actuators over the weekend. piece of cake and the noise is gone and the 4x4 works like a champ.

https://www.f150online.com/forums/ar...then-some.html

https://www.f150online.com/forums/20...replacing.html

 

I changed the selonoid today and it did not help.
Funny thing is that I never have and still do not have any trouble putting the truck into 4x4H ot 4x4L.
Took it for a drive after installing the new selonoid and the whining noise is still there when truck is in 2 wheel drive. Put it in 4H or 4L and the noise goes away.
And yes it gets louder the faster you go.
Any more suggestions???/

 

Are the IWE's the same for the STX with the manual transfer case shifter? Does it use the same system as the others with the switch in the dash?

 

did you do a leakdown test on the vacuum system? if you have a leak in the system, whether it be in the lines, at the vacuum box, or a bad check valve, the system will not work properly and will try to engage 4wheel drive when driving in 2wheel drive. click the link i provided you in my last post titled "everything you ever wanted to know about the IWE system" and you will see on the firts page the procedure for testing the entire vacuum system. i had a bad actuator and a bad vacuum line. replacing the actuator alone did not solve my problem. once i fixed the vacuum leak in the line my problem was solved.

 

The leak test will be my next venture, however it will be necessary that I wait until I start the physical therapy that my shoulder surgery requires. I am until then one armed and still in a sling. Fortunately I can leave the vehicle set as I can not drive either.. Not too happy about it, but it is what it is.

 

mine did the same thing...on 2004's there is no shield on the solenoid so water gets in and runs down the vac lines. My IWE rotted from the inside because of the water and it broke the spring. When driving down the road and the IWE spring breaks, the hub will partially engage, making that crazy sounds that gets louder with more speed. The reason your sound went away is because you stopped vaccum when you engaged the 4x4 and let the hub fully engage! Gotta get the revised solenoid with the shield, rip the IWE out and replace with a new one.

Both of mine have gone out this same way, I sprayed a touch of silicone lube into the vac hole on mine just to prevent rusting. Hope that helps

 

When my vacuum line busted that went over to the drivers side. I had no problem sticking it in and out of 4wd either. The drivers side was always trying to engage (since there was no vacuum to that side), only one that wasnt was the passenger side (it had vacuum). When I put it in 4wd the passenger side would lock in then the drivers side could lock in all the way too. The vacuum line runs down to the passenger wheel then around the front of the truck to the drivers side. The vacuum box should be under your battery (this is where mine was). Might want to buy a vacuum pump/brake bleeder kit from advance auto parts or where ever you like to shop (cost around $50) to test the IWE for leaks.

Why cant ford go back to a tried and true system (manual hubs or even the junky automatic hubs) and cost a lot cheaper to replace/fix.

 

just had my IWE solenoid replaced today by Ford under warranty on my 07 Lariat. It got fried out last week at the car wash!! it had the new style in there with the hood on it. so there (in my opinion) still some design flaws with these things!!

 

UPDATE:

Would like to thank everyone for their input, and with the assistance of a very good friend who owns a tire shop, and $140.00 later,I have a new IWE on the passengers side. The old one actually started crumbling apart when he removed it. Surprising to me since I only have 40,000 miles. (2006 FX4)Now that I think about it, several times in the past I had sometimes noticed a slight squeal or dragging metal sound intermittently when I would be next to a retaining wall or in an underpass. It was not always noticeable so I really thought nothing of it. Think I will do the other side once I am able to crawl around under it again.