Not what i expected inside at all... more research to do...A quick search and I found this. Pretty interesting BUT I’m going to spend some time later today investigating the non automotive rattler type dampers.
https://vibrationfree.co.uk/wp-content/uploads/2019/09/Pendulum-Damper.SecretsOfSpeed.pdf
The thing that always surprises me is guys running (including myself) 30+ year old rubber type stock ones and they still hold up most of the time..