Need help identifying a sound
 

Hi everyone. I am fairly new to the diesel engine group. Bought my first diesel truck (used) to have around the farm. So far loving it. However I have noticed a noise has started happening. I can't for the life of me tell where is coming from, the engine or the transmission or the differential. I recorded a video of the noise which only occurs while driving. Please take a listen and let me know what your best guess is on what needs fixing.

Truck specs:
03 Ford f250 XLT

Sounds drive train related to me, does it change pitch if you have it in 4x4?

Reminds me of a blower motor about to go south but it's not that for sure, and increases and decreases with road speed the way it sounds.

Can you hear anything under the hood at all?

Can't hear anything under the hood. Only happens when I'm driving, and not all the time. Just sometimes. My truck doesn't have 4x4, so I can't test that out. When the noise starts, I can coast down a hill with no engine rev and the sound still does its thing. I worry that it's transmission related....

Well, that takes the front diff and transfer case out of the equation then. Could be something like the output bearing on the trans........I don't know that a rear diff will make that kind of sound.

I'm going to throw a few thing out here, rear pumpkin gear oil? = universal gear
Front drive/ reverse drive tranny plates= transmission rebuild , brake calipers / bearings.too loud for the turbo besides not experiencing turbo lag? Have you checked for codes could be a Trans code.

​​​​​​yea not turbo related from what I can tell, def no lag from them for sure. I have not checked for codes yet. Brake calibers or bearings is interesting.... Not sure they could make this sound but if so that would be great instead of a tranny issue lol.

Happy Thanksgiving to all!