E350 Ford Super duty Box Truck

I have a unique noise from my truck that sounds like fluttering rather loud at almost all speeds even when the engine is off in neutral coasting.

Had the front end done checked U joints and DIff…all good. 19,000 miles. Sounds and feels like you have to open a window to relieve air pressure but that doesn’t not help. Tranny was checked too.
I’ve been on many BB sites noone can figure it out but its annoying. I have a big box truck with a translucent roof that ocilates a little bit but I’m not sold that it is the roof yet. I almost bought a wind deflector thinking that could be the problem…(wind) but not sure yet because I hear it at even 3MPH its crazy

I’ll take any thoughts

Does it make the sound if your just sitting in the unmoving/not running truck on a windy day?

Have you checked under the hood for a loose piece of plastic? Are you sure all your doors close properly? Our Chevy Express has one either door or window that doesn’t close properly so it always makes the sound like a window is cracked open.

I would have a look at the “doghouse,” the big cover in the middle of the floor that seals the engine opening where it comes into the cab.

Check the wheel bearings. Robin’s car had much the same problem, and it was almost unbearably loud at speed. Sure enough, that’s what it was.

Note that the F-350 has a full floating rear axle, so it could be rear wheel bearings as well as front, but the rear are supposed to run in a bath of 90W, so seldom give trouble.

It could also be a warped brake rotor.

Try to determine if it cycles at the wheel speed or faster. This will tell you if you need to look at above suggestions, or farther up the driveline (like U-joints, which are fairly cheap to fix)