Actually the PBT pinging on some boards annoys people pretty bad. It doesn't bother me to be honest but some people really hate it. It makes a little higher pitch noise which I think some perceive as a lot louder.
Yeah OK.
softer material = softer sound
although plenty of other things are more decisive than keycaps material
0.0001% refers to chance that they chose ABS keys so the keyboard is more dampened.