Tires sound like they have sand in them?

was checking my wheel bearings yesterday and spun the wheel...and i hear what sounds like sand inside the tire.
no idea what the previous owner may have done, but this is an unfamiliar sound for me. it's definitely not the bearings because you can stop the wheel from spinning and hear the material fall down the wall of the tire and settle at the bottom.
thoughts?

player.vimeo.com/video/265428496

Balancing beads? Never liked the idea.
Steve

thanks steve, what an odd concept.
the tires are old and hard so i'll probably ask the shop to balance with rim weights when i get those changed.