I dumped the CVT fluid and got some 80-90.
I started noticing the noise at around 8300 or 8400 miles, and it has 8800 today. That was the 4th this month. It started not as noticeable, like with my face shield down I couldn't hear it. But for the past week it hasn't gotten any worse. It is kinda jerky at low speed, like a flat bearing dragging or gears slipping. I still have to go borrow an impact to take off the clutch and get in there. Anyone know how to take the gear box apart on a Linhai 300?
I had another crappy problem today. Drove it to Ace to get gear oil, and I turn the key and it keeps running. I kill the engine, and all the lights stay on. Had to get a jump when I went to the grocery store. It's always something.

Sounding more like a mostly broken off gear tooth. The clack, clack, clack is from gear teeth slipping or skipping and banging up against the next good tooth. At slow speed there is more time for good teeth to slip/skip past the empty space. That squeaking noise sounds like gear teeth ends grinding against the broken edge and pushing at the tooth either side of the gap (depending on acceleration or deceleration) since there is not full meshing contact. The chipped/broken tooth is being eroded.... That is my interpretation anyway.

Think Car starter problem of teeth missing from the flywheel. At some point more teeth are going to break off. And it would be possible if positioned just right, the bike would not move because there is no gear meshing to drive the rear axle...... until the bike gets rolled and the gear turns enough for teeth to start meshing again... Of course with the skip and clang effect even worse.

If that is not what is happening and I have misinterpreted the description and videos, then it could be the (very bad) bearings after all.

Here are 2 videos where bearings and some performance gears are replaced on a KYMCO Super9. Access to the gears may be different than this for your bike, but again, the steps are going to be pretty much the same.

1) remove covers to gain access to clutch
2) remove drive belt and clutch
3) remove rear wheel
4) drain transmission
5) remove final drive transmission cover to access gears
6) pull gears to access bearings
7) pull bearings needing replacement
8) clean case of foreign material before replacing bearings
9) clean gears before replacing
10) after bearings and gears are installed, the rest is essentially reverse order of steps 5 to 1.

Some of this work may require some specialized tools especially if replacement gears are needed. However, stock shafts with the the necessary gears already installed might be available. Not sure with this bike. A service manual would really be helpful to do the examination parts of this at least so that you'll not be clueless if you take it to a shop for repair. It will be essential for proper procedures and torque values should you decide to do the work yourself.
HTH
https://www.youtube.com/watch?v=A-mvewH-e1A
https://www.youtube.com/watch?v=saroOZYidT0

I had strange noise from the rear of my 250 last month. Here is how the noise was isolated while spinning the rear tire.

1. Remove the brake caliper (noise still there)
2. Remove the swing arm (noise still there)
3. Remove the drive belt (noise still three)
4. Remove the centrifugal clutch (noise gone)

Problem was the ball bearing in the centrifugal clutch was going bad. The roller bearing was still good.

In your case, if removing the clutch you still have the noise only leaves the final drive.

Saw your video, your right to be alarmed! The rapid speed of the rhythmic clunking is key. The member that rotates at that speed is your culprit. Probably not wheel bearing, possibly a roller bearing inside the clutch hub assembly. Check the easy stuff first, and do any checks possible with the cover off to get closer to the origen of the noise. Use a long screw driver as a probe and put your ear against the handle. This is like a stethoscope. Rotating noises like that can fool you so take time to diagnose it.
Don't want to jump too far ahead but that sounds like a chipped gear that is constantly in mesh, and every time the chip meets its mate- you get the clunk sound. From the speed of the noise it's likely internal trans gear noise. But check EVERY thing external first.

It almost sounds like the cage is broken in a bearing somewhere and the balls are shifting at a certain point.

Was the problem found and fixed? Update please... Curious minds want to to know.

I'm sorry y'all, been busy with more crap going wrong. I found the problem, it was a stupid spacer, the one on the end of the clutch that goes into the bearing in the cvt case. It was loose and rattling around and I also think the bearing was a little cruddy. I put some grease in the bearing and cleaned the spacer, no more noise!

I had a problem where the electronics were staying on when the key was off. Seems the connectors melted together and shorted out the system. Stripped them and put them together, fixed! Now my CDI died, waiting for one from eBay.