What do you think causes the crackle and clicks we hear?

I can’t answer the why. I don’t know what causes the clicks and pops. I do know that a good cleaning helps. I use an RCM and I do a rinse and vac after using a cleaner. I use pure distilled water to rinse even though I’ve been told the water molecules are too big to get in the grooves. All I know is it works. And I will do just a water rinse if there is a lot of static on a record. The moisture kills the static. A Zerostat works well for me if the static isn’t terrible. I’ve noticed some of them work better than others. I think there quality control was never great. And there is a proper way to use it that I see most people get wrong. Youtube has plenty of examples of how to do it right. I still have some LPs with noise I can’t get rid of. I either live with it or I find a better copy. 

@mijostyn

If I could post photos I would, I have over 300 JPG files of groove images and all show carbonate in the bottom of the groove. so not sure what grooves you have looked at.
All I am doing is trying to remove some of the mystery behind LP cleaning and show more that getting clean LPs requires a bit of work if you are using VAC or US type cleaners, and can be done.
Have not tried the sink wash type cleaners so can't offer any insight on them.

If anyone wants to do a simple test, its quite easy. can be done on a vac machine (VPI or NG). use your favorite cleaning solution, apply it to LP. spread evenly across the LP surface.  Let is sit for 10-15 min then vacuum off.
Go play the LP. you will notice a much quieter background.


  

use your favorite cleaning solution, apply it to LP. spread evenly across the LP surface. Let is sit for 10-15 min then vacuum off.

@johnss   That sounds simple enough, I'll give a try shot.
 

These clicks, etc. are caused by a good stylus that tracks the imperfections, or a bad one that does not .