how do you check axle U-joints

Tomorrow I will be putting new brake lines front and rear, a coil spacer up front, and some RC drop brackets on my Jeep. I have been having a rubbing noise coming from the front of my Jeep when I turn to the left. I have to be making a good hard turn at speed, at least 20 or 25 mph, for this noise to be heard. I know some of you might say that it is a tire rubbing a control arm, but it's not. Yes my tires rub the LCA's, but I don't have to turn the wheel that far to make the rubbing noise. If I'm going slow, and have the wheel turned the same amount as I did when I heard the noise going faster, I will not hear the noise. I have looked under the hood and have found nothing rubbing.

If it's not the U-joints in the axle, what could it be? If it is the U-joints in the axle, how do you check to see if they are worn out? Are they hard to change? How much should they cost?

I'm willing to bet the tire is rubbing something else (fender most likely).

the noise is worse when in 4x4, and then you also hear it when going straight

Get underneath the heep, grab the front driveshaft and turn it both ways. There will be a little play in the shaft but look at the u-joint. There should be no play at the joint itself if you see some play its bad.

I know how to check a driveshaft U-joint, I'm talking about the ones in the front axles. They have bearings and U-joints in them. How are they checked?

Could also be the hubs, had this problem on my 90 T-Bird (first car), made a rubbing sound at first and turned into a grinding noise after a while. only happened when turning left or right (don't remember) and put load on it, ie going 20+. Searched all over looking where it was rubbing, then when it turned into a grinding noise took it to a shop found out it was a bad hub. I had both replaced at the same time. Noise was gone.

I would check them the same way, only while turning the DS observe the U joints on the knuckle ends for play. This works best in an open axle since a locker would complicate this simple test. You could also put it in 4x4 and make sure the front is engaged, park it and raise one side of axle up enough to turn the tire. Then have someone turn that wheel back and forth while you observe the joints for play. This is just what I would do, not knowing what else proper to do to find out. If I found play that would mean a visit to the partstore for me.
Now what to do about a loud squeeling from my axle? I did this u joint check and all is good and fluids where they should be.