Well I went threw quite a few posts in another forum - it's never really pin pointed, but from 2004 -2006 it 's a pretty big problem.

From what I gather, a few have tracked it down - it's coming from inside between the vent and the window. Here's one post of a temp resolve -

"i read this post the other day, the next morning, i noticed a "buzzing" noise. i have about 2500 on mine, this is the first time i noticed it. however, that was the first time that i did not let my truck warm up for a few minutes befor leaving. having just read about this the night befor, i took a min. to try and locate. while it sounded like it was under the hood, mine was comming from the windshild, dash, and d side a pillar area. i wedged my finger tips ovet the vin tag, pressed down on the dash with the heal of my hand, and braced my fore arm against the a pillar, and the noise went away."

BTW - Someone also mentioned a TSB was issued - I'll be damned if I can find it...

 

i appreciate all of the timethat you are putting into my post. and people may call me crazy but i really believe in my case that it is the instruement cluster making the noise. mine makes this noise if say i am coasting at 25 mph and then hit the accelerator real quick and continues to make it until either i let off or then rpms reach the point where the engine drowns out the sound. again whenever i do the guage sweep all of the guages sweep, but the noise that they make is the same that i hear on acceleration. also looking at another postreminded me that on several occasions i have filled the fuel tank and it took around thirty miles worth of driving for the guage to register full. the keys were out of the ignition during filling and i'm aware that it could possibly be the sending unit? Also, i remember one of the guages "twitching" while driving down the road, but i can't remember which one it wasn't the tach or speedo. at first i thought my eyes were playing tricks on me and i was cruising on a flat road.

 

That sounds like a fun one to find . Off the top of my head - Could be a bad relay. I would check them all (even under the hood in the PDB), loose fuse block under the dash maybe, cracked solder joint on the backside of cluster, a bare/shorting wire ..?..

Just a few things I might check.

Maybe, if the dealer re-flashed the PCM it would go away ..?.. I doubt it :o

When you get her figured out , let us know what it was

 

i do tend to have a good sense of humor, but with this one, iam at my wits end. i'm tired of listening to it myself and i'm tired of everyone that rides in my truck asking what the f##k is that noise?

 

The fuse block and relays are located on the lower passenger side kick panel, sounds like it may be closer to the IC.
There is a bulletin out for eratic fuel gauge operation..TSB 08-2-9. That may be part of the problems but usually they sending unit failures do not cause any noises in the dash. I've replaced a pile of sending units on the whole Ford product line...VERY COMMON
A Reflash as mentioned will most likely not fix your noise but could cure your poor throttle response There are a few messages out for that one, there were a lot of complaints about that when the F-150's went to electronic throttle control.
It's definitely a tough one to track down over a forum without actually hearing...good luck with it...definitely let us know what you come up with.