When a vessel is empty, if you tap on it or drop it, it will make far more noise than if it contained something. Even a small quantity of something in it will create less noise than if it were to be totally empty.
The proverb 'Empty vessels make the most noise' is used to refer to a person or persons who, despite having the least knowledge of something will talk about it to the maximum. Such people are also the ones who make the most arguments or create a ruckus over an issue.
1. Medha was getting increasingly annoyed with the new intern. He always butted in when the seniors discussed the project and was akin to an empty vessel making noise.
2. The passengers were amused at the British tourist ranting about the flight delay when all of them were well aware of the fog causing the delay. He was just an empty vessel making noise.
3. The politician's aide advised him not to be an empty vessel making the most noise during the TV interview as it would reflect badly on him.