Whistling tube noise?

[Fordalways]

...
It's movement, not engine related - I can rev when stationary, and it doesn't matter. Don't think it's brakes either. Happens when moving (forward or reverse).

Changes note with speed - up or down ...
What should I check?

Since the OP says it’s heard in reverse as well as forward that likely rules out wind noise. Expect it will be mechanical and noises can be telegraphed through the body making it difficult to isolate from the driver’s seat. 4WD or RWD? May have to put it on a frame lift and start turning things to narrow it down. As others have mentioned, a wheel bearing is likely. Any evidence of leakage around the diff or wheels?

 

[alexwasserman]

It's a 4WD, and it's in 4A mode.

Thought about moving it out, to see what changes. Worried that'll f stuff up worse.

Will have time to mess with it this weekend when I can jack it up and take the wheels off it.

 

[flyguy]

We had a whistling sound with our 2015 XLT Expedition. It wasn't motion related; it began when the engine started and would stop if I opened a door. It turned out to be the rear side window - it wasn't completely sealing, allowing a small, high velocity air flow. Use some Armorall on the seals to fix the problem.