They are not magnetic. I have a magnetic puck shape with steel ball bearings that does just as you said Frank
I use the bearings to clean decanters then back on the stand, no losing my bearings
Weird little bleeders have a soft sound if that makes sense, they dont get bottlenecked when turned upside down like an egg timer but flow very freely. Lead would have been my first guess but as you say it would be very messy, unless they are covered with some kind of coating. I will recheck the weight at mine when I get home. I like the weird pieces like this even if we never find out what it is.