What exactly causes clicks and pops on vinyl?

The surfaces of vinyl records are fragile. Many people simply will not admit this simple fact. When the surface is damaged from physical contact with anything, including a stylus, it will have scratches, gouges, indentations and such. If you consider that a great many records are not pressed very well to start with and are otherwise mishandled at the factory (glue from the sleeve finding tis way on to the record is one such example), you have another bunch of LPs with noise issues.

The other source is something you can do something about to a certain extent and that is dirt. I include in "dirt" the oil from finger prints. A simple solution there: never touch the surfaces with bare hands, always handle LPs by the edge and by the label.

Audiophiles have now accepted that vinyl records must be washed with some sort of solution and scrubbed by some sort of contraption.

I still believe in cleaning records with a carbon brush only to avoid a chemical deterioration of the vinyl.

If silver discs are not starting to look more attractive by now, you are a committed vinyl freak and very trendy person!

dust, and inclusions in the vinyl when pressed, and scratches across the surface.
The inclusions get there from poor quality recycled vinyl being used to make the record.
The dirt gets there deep in the grooves from improper handling and poor maintenance.
The WORST possible cleaning sprays the surface of the record, then wipes off the surface, without drying, or deep cleaning the grooves. Then, all the crap in the grooves that cound have been removed easily, turns into a compressed hardened layer of difficult to remove crud.
Playing a record in this condition makes the stuff even harder to get out.

Clicks and pops heard during playing vinyl record are caused (beside factoy defects in new vinyl) by (1) "added portions" in the record groove (dust, dirt particles) or (2) "missing portions" (scratches). In the first case cleaning (dry with carbon brush or washing) would avail, in the second case there's nothing to be done.
Some (two to five) sudden louder pops are as often as not caused by stucked particle of dirt, which can be removed (by wood toothpick, for example).
To Pbb - sometimes record washing is unavoidable, mostly with second hand records (from careless owner).
Jan, if you can not afford a record cleaning machine, hand wahing is still at yous disposal.
A.

Agree w/most of the above. So with your budget, here's what you do"

Buy good liquid cleaning system from either Walkeraudio or Audio Intelligent. Get good velvety-surfaced cleaning brushes(Disc Doctor or Mobile Fidelity).
Buy a couple of large white thick cotton bath towels.
Buy a plastic dish drying rack from Target/Walmart.

Place the clean towels on a large table. Clean by hand per intructions. Air dry in the dish rack. You can clean about 10 LPs at a time, in about 15-20 minutes, and they will dry in another 15 minutes. Place the clean LPs immediately in a brand new good sleeve(search archives or just go to Elusive Disc).
When about to play LP, swipe it with an Audioquest Carbon fibre brush to remove static and stray debris.

This isn't perfect, but it will get you surprisingly far until you can get a vacuum cleaning machine. Cheers,
Spencer

At the time of pressing, release agents are used that can/will collect dirt from the atmosphere and the cheap paper liner records come in. That's why it's good to use one of those nice record cleaning machines before ever playing the disc(bought my VPI back in the day for $325.00). When your stylus winds it's way through the groove, it actually melts the surface just as skates do to the surface of ice(just talking a few molecules here). If not cleaned prior to play- particles of dirt will be welded to the groove walls. These of course make noise and wear your stylus. Before I ever played a record(usually tried to find virgin vinyl pressings, MFSL, Crystal Clear, Sheffield Labs, Telarc, etc), I'd use the VPI, treat the record with L.A.S.T. after drying, let that sit awhile and finally: use my Discwasher brush on it. My records are stored in rice paper liners. Cleaner than paper, and they don't leach the elastomers out of the vinyl. Sound anal? The records I purchased over twenty eight years ago are still pristine, and I've gotten excellent mileage out of my styli. At very least: find a Discwasher brush and liquid, clean your discs b4 each playing, and don't scratch(OUCH) or touch the grooves with your fingers as Pbb said.