[bandito2]

Possibly rollers/sliders are not operating properly or maybe not correctly installed in the variator. Maybe rear wheel out of balance.

(or maybe the gremlins get mad at the noise and jump up & down) just kiddin
But you should check the variator since it sounds like the last thing that was done to the bike.

Often, things that were changed are the culprits to the problem. And that is why the sage advice is given to change/modify only one thing at a time and test it and make sure it works/does what you want it to do. Changing too many things at once can send you on a wild goose chase trying to track down and resolve problems.

Not saying you changed too many things... just putting it out there since it is something that sometimes happens and advice to help keep one from needlessly creating their own problems.