I did a few searches on this...
Wheel does not have play, so can I rule out U joints, and maybe focus on Trac Bar? If I am about to replace my Axle seal, should I just do the u joints while apart? thanks

 

Is it doing it when you turn the wheel sitting still or while driving? And do the ujonts with the seals or you will just be doing the same work 2 times.

 

Most likely axle u joints have too much play.

 

Is it only when you turn one direction? Also, is it a constant knock or just one knock?

 

I want to say both directions, turning slow like parking. And just one knock.

 

Check the track bar mount at the axle. My bot was loose and it caused a sound similar to what you describing. Have someone turn the wheel back and forth while you watch it. If that's not the problem you should be able to see the problem.

 

I agree most likely a bad trac bar bushing