What exactly causes clicks and pops on vinyl?

Something else that helps is to avoid phono sections that employ any sort of loop feedback. A zero feedback (passivly equalized) phono preamp will tend to make less of the ticks and pops fed into it. I have seen it be the difference between 'annoying' and 'nearly silent' (in extreme cases). BTW most zero-feedback phono reproducers will be vacuum-tube.

Atmasphere,

There is another thread on Audiogon that talks about record cleaning rituals that includes a lot of different ideas about how to get a record clean.

The most deadly kind of click or pop is due to a scratch on the record, meaning the physical surface of the record has been gouged or damaged, most often by some wayward or accidental bumping or moving of the stylus ( the tip of which is much harder than the material that the record is made of and hence scratches it upon contact). Of course there are many other ways to scratch a record as well. A scratch of this nature will often be evident upon close inspection as a sharply formed linear feature on the surface at some angle to the direction of the grooves. Stay away from used records that evidence scratches of this nature because there is not much you can do to fix it once damaged.

Defects in the cutting of a record (defective grooves) often manifest themselves in the form of other types of undesirable noise or distortion. These are generally harder to detect upon inspection, but with some practice and trial and error, it is possible to spot many vinyl albums with groove damage in advance.

Foreign material on the surface of the record also produces noise of course, and can also accumulate in denser clumps that manifest themselves sonically as a pop or click, though not a visible scratch. A good cleaning can usually put an end to this kind of problem.

Hope this helps.

What I would add to much that has been said is that on top of the various sources of foreign material and defects is that when the stylus moves across the record it is putting a great amount of force on the vinyl that in fact heats each grove in the vinyl to hundreds of degrees for an instant. So on top of all the stuff on the record the environment on the record is pretty harsh.