It's usually segregated as clicks vs. crackle with crackle being much smaller and more numerous clicks. They result from poor quality pressings and/or poor handling. I believe Atmasphere draws a link between how audible and annoying they are with phono stage overload characteristics.
What do you think causes the crackle and clicks we hear?
I think pops are easier to understand but clicks and crackle noises, what causes this?