This is not exactly the same as your examples… Especially the first one, but maybe it’s close enough.
- Start with a white rectangle
Effect > Artistic > Sponge...
- Definition and smoothness should be quite high.
Object Expand Appearanceso that you can trace it.
Object > Image Trace > Make...
black & whitepreset as the starting point.
- Adjust the threshold and other sliders if needed.
- Expand it