If you want to make your Z-Stacks quieter, put some thin lube in the stack bearings.
To take off the stack part, stick your finger in between the yoyo and stack, and pry it out. There are probably other methods, but I don’t know any others.
Oil for instruments works very well for lubing your yoyo! If you go over to a local music store, just ask for some rotary oil or some trumpet valve oil.
It is thin enough so that it does not slow the bearing down too much but still effectively gets the job done.