i dont know if this is the right place to ask, but this is my first zbrush scuplt and i need a little help with some things.
When using mirror and weld my model doesnt really weld as seen in the image below. Is there a way to fix this?
And number two, when using a surface noise modifier the hex shapes get distorted, is it because of bad geometry? how can i fix it? 
Unfortunately, it looks as if your model has been moved slightly off-center. You’ll have to move the model back towards the center slightly until you get the mirror and weld result you want. Unfortunately, this will require some cleanup after the fact.
Were you working on the model as a half previously? It’s possible you may have sculpted or smoothed the model off center. Always try to work on whole figure. If working symmetrically you only need sculpt on one side or the other, but keeping a whole figure will at once will help you avoid this problem.
you’re right maybe i messed ub by moving my model around too much, but thanks anyway. do you any idea how to fix the surface noise deformation on the model?
small_orange_diamond
If your model is UV’d, you should tick the UV tab in the Noise Window.