Got an '03 F250 2WD with the 5.4l and AT. In the last couple of days the intake has started making a loud, obnoxious moaning from time to time. Kinda like a jetty foghorn or when you blow across the mouth of a beer bottle. And it's loud enough to give you a headache if you stand in front of it with the hood open for too long. Sometimes if I blip the throttle it'll go away for a minute, sometimes not. There's no real pattern to it.
I was outside checking it out a minute ago while it was moaning, and suddenly there was a *CLICK* and it stopped howling like somebody threw a switch. Then it gradually came back again. When it was moaning in full force again, I started feeling around the radiator and engine, and the noise seems to be centered where the cold air intake is on the driver's side of the radiator. There's also an intense high-frequency vibration I can feel on the plastic air intake assembly. I popped the filter housing open and took the filter out, but it didn't make any difference. Whatever it is seems to be coming from way in there, like the throttle body or IAC motor. It's resonating all the way up to the end of the air intake and turning it into a megaphone.

I need to do some more investigating, like checking the vacuum-driven stuff such as the A/C and heat controls, but I wondered if anyone else has run into this before.
One good thing about it is that it will scare deer and elk off the road from a half mile away, but that's a small consolation for losing your sanity.

 

Do you have a flat pancake type thing inline in the hose between the IAC and the main intake tube?

That thing is a one-way valve, I think... I'd imagine it could moan a lot

Maybe remove it or just crimp the hose when the moaning is occuring to see if that's the problem.

Crimp other things too, like the vacuum hose going to the master cylinder power booster. Be careful

 

Sounds like the IAC

 

I just got a PM about this from somebody else, so I figured I'd respond here.

Like krewat said, there's a dealy-bobber that looks like a check valve on that hose. I haven't looked at it in a long time, but I thought it was between the airflow sensor and intake, but I'm probably wrong. It's on a shop truck that I don't drive much, and I've had 1000 other things to do at work all summer.
Anyway, I pinched off that hose, and the noise stopped. I let it go, and it started to build up noise again. I disconnected the hose, and the engine immediately died.
The thingy looks like a check valve that's on the Thermactor system on my Bronco, so I suspect that's what it is. I tried to look it up in a Standard Ignition catalog, but couldn't find it. I plan on pulling it off and getting the OEM number off of it, but I haven't got around to it. If it was actually my own truck, I'd be living in an adult foster home and wearing a drool bib after going nuts from listening to it.
WOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOHHHH HHHHHH!!

You get the idea.

 

That piece in the hose is to break up the airflow and to help to reduce this sound. I have never seen one fail ever. Again it is likely the IAC.