In this topic Jeffeb3 posted a YouTube video of a sand table build. The video author suffered through some of the same struggles you indicate here. One takeaway for me was the use of a felt pad on the bottom of the ball. the felt ought to significantly reduce noise, and the felt on the ball and perhaps on the magnet below would allow some adjustment in distance and therefore to magnet strength.
Some cool ideas in your build. I look forward to future updates.