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

I have the same issues with these old records I am cleaning using the SpinClean record washer.  Most show a lot of improvement in amount of noise, but there are certain records that continue to pop and crackle.  I clean them a second time and not much improvement.  I was chalking it up to excessive grove wear — I know that the equipment they were played on decades ago was not very good; neither was the care and cleaning (some were my teen party records).  I hadn’t thought about static electricity.  I will need to look into that.

On another thread, I asked for advice for reducing the warp in one record that I have. I think it was affected by heat somehow.  My idea was to use a clothes iron to heat the record and press it flat.  I laid the record on a paper record sleeve on a flat surface, then placed a microfiber towel over the record and then applied the iron (no steam).  I went slowly and started out with low heat.  The warp decreased but not enough to play it.  So, I gradually upped the heat and it was still hard to get the record flat — If anything, it warped more on other parts of the record.  I think it would take a special device that could apply heat and pressure equally over the entire record surface all at once.  Otherwise, it just continues to warp in a different way than when you started.  I was looking forward to hearing those island rhythms too!

The Zerostat has always been a pain to use, and only marginally effective. I replaced it with a Nagaoka Kilavolt No. 103 (no longer in production) years ago, and now also have a Furutech Destat III. Both are much better than the 'stat.

Hi,
even if you have a turntable with acrylic platter and there is humidity.

For me, it's my bones! Joe

In my case, most of the records that I play are new re-issues. I use an anti-static fiber brush and zerostat, but these are only marginally effective. The VPI vacuum doesn't get much work unless I've picked up used records from the local bookstore.
I have noticed that the clicks and crackles are mainly on my TW Acustic especially when I was using the copper mat on it, the issue is lessened a great deal since I've gone with a different mat on this table but still present. The copper mat doesn't seem to be problematic on the two Garrards though. My guess is the TW setup is just more prone to static for some reason. It could also be a tonearm/cartridge resonant issue, but I haven't narrowed it down yet.
I don't think phono overload is the case here since the noises were present with a Pass Labs, a Jasmine, and a King/Cello phono stage.