Ok, not exactly an F-150 but a this is a 91 bronco, the f-150's little brother with a short frame and a hard top. This has the 351w with the E40D 4 speed automatic, and 4x4. While driving, it makes a horrible squeal/whistle that changes pitch even while maintaining a constant speed, it does it in every gear, including neutral, engine rpm doesn't effect it at all, it also does it in 2wd and 4wd, and it doesn't do it at all on jack stands, also, the front and rear drive shafts are getting hot. Here's a link to a video of it:
P.s. I know there's a bronco forum, but I already had this account, and there's a lot more people here. Lol

 

I had a truck that would make a noise close to that. I would have made the same post you did in describing it and what I had looked for. It ended up being the windshield. There would be a change in pitch if the wind was blowing. I ran a small bead of silicone between the trim and glass to stop it.

 

Thanks, but this is more like a metal on metal screech, it does it at around 15 mph and over, it gets louder at higher speed, and almost smells like burnt grease.

 

Odds are nobody will be able to come on here and put their finger on it right away.

Throw some duck tape on around the windshield and over the gap between the door and the a pillar just to knock that off the list of possibilities.

Never heard that noise before...

 

Whew, that's a tough one. Some off the wall ideas are loose windshield trim, the rear cap (assuming it has a removable bed cap) not snugged down tight, maybe the tailgate pin grommets are worn or gone, or something with the exhaust hangars. Still can't make the connection between the noise and smell of burnt grease...

Good luck and keep us posted. The solution would be one to file for future reference. :-)

 

Have you checked transfer case fluid? does it have lock-outs ? Might cause driveshafts getting warm. Stab in the dark.

 

I'll be damned, it was the light bar! Of all things! It was whistling! The burnt grease smell? Oil leaking on the exhaust manifold, the hot driveshaft? Muffler getting really hot and heating up everything near it. :facepalm:

 

The problem was that wind was passing over the cooling fins and making them vibrate at a high frequency, I made a temporary solution by putting small pieces between the fins in the middle to stiffen them, I'll need to do a more permanent fix soon, As you can see, the former owner of the truck attempted to fix the problem by caulking the left side of the fins, this was obviously unsuccessful.

 

Apparently this is a problem with lots of light bars.

 

Not far from the windshield. That drove me nuts until I figured it out.