Find a spot where you can drive close to a retaining wall or building in a quiet area.
Use this wall or building to determine if the noise is from the front or back , left or right.
Just do the same thing that makes the noise appear with the windows down the wall should reflect the noise back to you.
Or just get a friend and tie strap him or her under the truck
Wheel bearings normally will make more noise while turning from side to side, so it is not likely your problem.
Ujoints could be the issue but it is hard to tell by your description.
It is easy to inspect the ujoints if you think they may be the problem.
For now check all the basics regardless if it may be the cause of the problem or not. I would inspect the bearings for play just in case, check the brake pads and shoes and remove the drive shaft to check for play and or binding bearings in the ujoints