Ok, what just happened? My turntable journey...thus far.

Great story - finding a good tweak like that is priceless, especially if it doesn't cost a whole lot.  IME, isolation is key in high-end audio.

Nice throw.

Can anyone explain what is happening here?

Yeah, sure. You got lucky. 

Ticks aren't really any different than the music signal, in the sense they make the stylus move, other than the way they are transients that come and go all at about the same speed and duration. Where music is chock full of transients that are all over the place in terms of frequency. 

The cartridge, all it does is generate a signal based on this energy. But it cannot distinguish between movement caused by the signal in the groove, dirt in the groove, and vibrations coming from the table and arm. The cartridge just adds it all together and sends the signal down the wire, to be amplified about a million times.

This is why when the question was asked recently which is more important the cart, arm or table the consensus was the arm and table. Your experience just now confirms this. What you just did in essence is improve your turntable. What you just heard is this outweighed a lot of other stuff you did including a much better cart and even a hugely better phono stage. 

But what you want to know is, Why? What is going on? I'll tell you.

All those vibrations, not just ticks and pops but music too, they travel down the arm and into the table and all the way to the feet and then into the rack- and no it does not stop there!

The rack is now vibrating only because it is vibrating in sympathy with the cartridge we call it ringing. Ringing happens with all kinds of things and is a major reason why Townshend Podiums are so incredibly effective. Ringing also happens in speaker cables (F1 are designed to minimize this) and other wires. Ringing is why MC carts sound bright until we load them down. Ringing is you might say a thing.

In your case the feet on your table and your shelf or rack were ringing a lot at just the right frequency to aggravate that is to say reinforce ringing in this frequency range. Where you got lucky, the cork was just the right material to break this cycle. Listen closely you will hear it is not just ticks and pops but the clarity and detail around everything in that same frequency range is improved. I imagine cymbals are a lot less tizzy for example. Sax you probably hear more reed and body now, no longer blown out by the exaggerated presence region.

When you try Nobsound be prepared to experiment because while they are pretty good they are broadband and not tuned to one narrow little band like cork. Same for Townshend Pods, which will probably be a lot better not only for the superior isolation and damping but also because they use a thin felt type material that probably performs similar to cork. Which is by the way pretty decent stuff- Mark Baker uses a very thin little bit of cork on his Sovereign turntable. But Baker is clever enough to use it as tuning (it is on only two of three feet) and a tailored thin slice at that.

Which is why the short answer, you got lucky. But at least now hopefully understand a little more of why.  

I got lucky when I switched to Sota 38 years ago.
Springs do a good job stopping the ring.

Isolation/damping is everything with a turntable. They will pick up literally any vibration. Surface noise, as mentioned, is part of the game. But sometimes those ticks and pops can be exacerbated by a poorly set up cart, or a mismatch. Nail down the vibration, then meticulously dial in your cart, and play with your phono stage settings as well to tone down the pops etc.